Linear Motion
Summary:
Practice Problems
Problems 24, 25, 26, and 29 are particularly challenging.
Review Questions
NEWTON'S FIRST LAW QUESTIONS (review questions)
Newton's First Law of Motion- Inertia (Practice problems)
Newton's Second Law of Motion (Review Questions)
Newton's Second Law of Motion - Force and Acceleration (Practice Probs)
Newton's Third Law of Motion- Action & Reaction (Practice Problems)
Newton's Third Law- Action & Reaction (Review Questions)
Summary:
- Speed is the rate at which distance is covered: Speed = distance/time, or v = d/t
- Instantaneous speed is the speed at any instant
- Average speed is the total distance covered divided by total time: v(average) = d(total)/t(total)
- Velocity is speed in a given direction
- Acceleration is the rate at which velocity changes with time: Acceleration = (change of velocity) / (time interval) or a = v/t
- Velocity acquired with constant acceleration from rest is acceleration multiplied by the time interval: v = at
- Distance covered from rest at constant acceleration: d = (1/2)at^2
- Acceleration due to Earth's gravity: g = 10m/s^2 (or more precisely, 9.8m/s^2
- For free fall, velocity acquired from rest is acceleration due to gravity multiplied by the time interval: v = gt and distance fallen: d = (1/2)gt^2
- If a falling body doesn't begin with zero velocity, these relationships are v = v(o) + gt and d = v(o)t + (1/2)gt^2, where v(o) is the initial velocity, and the + (positive) sign may be replaced by a - (negative) sign, depending on your choice of positive and negative directions
Practice Problems
- Find the speed of a baseball that crosses from the front to the back of home plate, a distance of 0.2m, in 0.01 s.
- Find your average speed if you run 50m in 10s
- A tennis ball travels the length of the court, 24m, in 0.5s. Find its average speed
- A bus travels 30km in (1/2)h. What is its average speed in km/h?
- How far will you travel if you maintain an average speed of 10m/s for 40s?
- A cyclist travels for 30 min with an average speed of 10 km/h. How far does she travel?
- What is the acceleration of a bus that goes from rest to a speed of 50 km/h in 10s? (Hint: You can express acceleration in units of km/(h*s)
- On a distant planet a freely falling object gains speed at a steady rate of 20 m/s during each second of fall. Find its acceleration.
- What is the acceleration of a ball that starts from rest and rolls down a ramp, gaining a speed of 25 m/s in 5s?
- An apple drops from a tree and hits the ground in 1.5s. What is its speed just before it hits the ground?
- On a distant planet a freely falling object has an acceleration of 20 m/s^2. What speed will a body dropped from rest on this planet acquire in 1.5s?
- A skydiver jumps from a helicopter hovering at high altitude. If there were no air resistance, how fast would she be falling 12s after jumping?
- An apple drops from a tree and hits the ground in 1.4s. How far does it fall?
- On a distant planet a freely falling object has an acceleration of 20 m/s^2. What vertical distance will an object dropped from rest on this planet cover in 1.8s?
- What vertical distance will a body dropped from rest fall in 12s of free fall?
- What is the instantaneous velocity of a freely falling object 10s after it is released from rest? What is its average velocity during this 10-s interval? how far will it fall during this time?
- If you were to walk with a speed of 2.0 m/s for 2.0h, how far would you travel?
- The ocean's level is rising about 1.5 mm per year. At this rate, in how many years will sea level be 3 m higher than it is now?
- The speed of sound in air is about 344 m/s. if you're seated 250m from home plate at a ball park, how much time passes between seeing a baseball being struck and hearing it? (Hint: Light travels nearly a million times faster than sound)
- Johnny Hotfoot slams on the brakes of his car moving at 60mph (26.7 m/s) and skids to a stop in 4s. (a) What is the deceleration of the car? (b) How far does it skid?
- Kenny Klutz drops his physics book off his aunt's high-rise balcony. It hits the ground below 1.5s later. (a) With what speed does it hit? (b) How high is the balcony? Ignore air drag.
- You drop your pencil from your desk, which is 1.0m above the floor. (a) How long does it take for the pencil to hit the floor? (b) How fast is it going just before it hits the floor?
- Tara Trucker is driving at 27 m/s through a fog that limits her visibility to 30m. She suddenly sees a car in front of her traveling in the same direction at 10 m/s. If she fails to apply the brakes, how much time does Tara have between seeing the car and crashing into it?
- You drive to the city at an average speed of 40 km/h and return at an average speed of 60 km/h. Find your average speed for the entire trip? Explain why the answer is not 50 km/h.
- Harry Hopeless averages 40 km/h for the first half of his car trip. How fast should he drive on the remaining half of the trip to have an average speed of 80 km/h for his trip?
- A train moves at a constant speed of 60 km/h toward a station 30 km away. At that moment Fanny Fastbird leaves her perch on the locomotive and flies toward the station at a constant speed of 100 km/h relative to the ground. When the bird reaches the station, she immediately turns around and flies back to the train at the same speed. When reaching the train she again immediately turns around and flies back to the station, repeating the process until the train passes the station. What total distance is traveled by the bird?
- Use the time-independent equation for uniformly accelerated motion, v^2(final) - v^2(initial) = 2ad, to solve the following: A rocket traveling at 40 m/s accelerates at 2 m/s^2. find its speed when it has traveled 200 m.
- A new test vehicle will accelerate at a steady 4 m/s^2 over a 500-m track. How long with the vehicle take to travel the track?
- When Valerie Volleyballer jumps to spike a ball, she rises a total of 2.0m in the air after accelerating through 0.5m (from crouch to full extension) What is her acceleration during takeoff?
Problems 24, 25, 26, and 29 are particularly challenging.
Review Questions
- What do we mean when we say that motion is relative? What is everyday motion usually relative to?
- Speed is the rate at which what happens?
- You walk across the room at 2 kilometers per hour. Express this speed using abbreviated units
- What is the difference between instantaneous speed and average speed?
- Does the speedometer of a car read instantaneous speed or average speed?
- What is the difference between speed and velocity?
- If the speedometer of a car reads a constant speed of 40 km/h, can you say that the car has a constant velocity? Why or why not?
- What two controls on a car cause a change in speed? What control causes only a change in velocity?
- What quantity describes how quickly you change how fast you're traveling, or how quickly you change your direction?
- Acceleration is the rate at which what happens?
- What is the acceleration of a car that travels in a straight line at a constant speed of 100 km/h?
- What is the acceleration of a car moving along a straight-line path that increases its speed from zero to 100 km/h in 10s?
- By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2 km/h*s? At 4 km/h*s? At 10 km/h*s?
- Why does the unit of tie enter twice in the unit of acceleration?
- What is the meaning of free fall?
- For a freely falling object dropped from rest, what is the instantaneous speed at the end of the fifth second of fall? The sixth second?
- For a freely falling object dropped from rest, what is the acceleration at the end of the fifth second of fall? The sixth second? At the end of any elapsed time?
- Toss a ball upward. What is the change in speed each second on the way up? on the way down?
- How far will a freely falling object fall from rest in five seconds? Six seconds?
- How far will an object move in one second if its average speed is 5 m/s?
- How far will a freely falling object have fallen from a position of rest when its instantaneous peed is 10 m/s?
- What does the slope of the curve on a distance-versus-time graph represent?
- What does the slope of the curve on a velocity-versus-time graph represent?
- Does air resistance increase or decrease the acceleration of a falling object?
- What is the appropriate equation for how fast an object freely falls from a position of rest? For how far that object falls?
- Calculate the average speed (in m/s) of a cheetah that runs 140 meters in 5 seconds
- a. Calculate the average speed (in km/h) of Charlie, who runs to the store 4 kilometers away in 30 minutes. b. Calculate the distance (in km) that Charlie runs if he maintains this average speed for 1 hour
- Calculate the acceleration of a car (in km/h*s) that can go from rest to 100 km/h in 10 s
- Calculate the instantaneous speed (in m/s) at the 10-second mark for a car that accelerates at 2 m/s^2 from a position of rest
- Calculate the speed (in m/s) of a skateboarder who accelerates from rest for 3 seconds down a ramp at an acceleration of 5 m/s^2
- Calculate the instantaneous speed of an apple that falls freely from a rest position and accelerates at 10 m/s^s for 1.5 seconds.
- An object is dropped from rest and falls freely. After 6 seconds, calculate its instantaneous speed, average speed, and distance fallen
- Calculate the instantaneous speed and distance fallen for an object that falls freely from rest for 8 seconds
- Why is it that an object can accelerate while traveling at constant speed, but not at constant velocity?
- Light travels in a straight line at a constant speed of 300,000 km/s. What is the light's acceleration?
- Which has more acceleration when moving in a straight line- a car increasing its speed from 50 to 60 km/h, or a bicycle that goes from zero to 10 km/h in the same time? Defend your answer.
NEWTON'S FIRST LAW QUESTIONS (review questions)
- Skip
- Skip
- What is the effect of friction on a moving object?
- The speed of a ball increases as it rolls down an incline and decreases as it rolls up an incline. What happens to its speed on a smooth, horizontal surface?
- Galileo found that a ball rolling down one incline will pick up enough speed to roll up another. How high will it roll compared with its initial height?
- Does the law of inertia pertain to moving objects, objects at rest, or both? Support your answer with examples.
- The law of inertia states that no force is required to maintain motion. Why, then, do you have to keep pedaling your bicycle to maintain motion?
- If you were in a spaceship and launched a cannonball into frictionless space, how much force would have to be exerted on the ball to keep it going?
- Does a 2-kilogram rock have twice the mass of a 1-kilogram rock? Twice the inertia? Twice the weight (when weighed in tbe same location)?
- Does a liter of molten lead have the same volume as a liter of apple juice? Does it have the same mass?
- Why do physicists say mass is more fundamental than weight?
- An elephant and a mouse would both have zero weight in gravity-free space. If they were moving toward you with the same speed, would they bump into you with the same effect? Explain.
- What is the weight of 2 kilograms of yogurt? (1 kilogram = 9.8 Newtons)
- What is the net force or, equivalently, the resultant force acting on an object in equilibrium?
- Forces of 10N and 15N in the same direction act on an object. What is the et force on the object?
- If forces of 10N and 15N act in opposite directions on an object, what is the net force?
- How does the tension in your arms compare when you let yourself dangle motionless by both arms and by one arm?
- A clothesline is under tension when you hang from it. Why is the tension greater when the clothesline is strung horizontally than when it hangs vertically?
- If you hold a coin above your head while in a bus that is not moving, the coin will land at your feet when you drop it. Where will it land if the bus is moving in a straight line at constant speed? Explain.
- In the cabin of a jetline that cruises at 600 km/h, a pillow drops from an overhead rack into your lap below. Since the jetliner is moving so fast, why doesn't the pillow slam into the rear of the compartment when it drops? What is the horizontal speed of the pillow relative to the ground? Relative to you inside the jetliner?
- If a woman has a mass of 50kg, calculate her weight in newtons?
- Calculate in newtons the weight of a 2000 kg elephant.
- Calculate in newtons the weight of a 2.5 kg melon. What is its weight in pounds? (1 kilogram = 2.2 pounds)
- An apple weighs about 1N. What is its mass in kilograms? What is its weight in pounds?
- Susie Small finds she weighs 300N. Calculate her mass.
- Many automobile passengers suffer neck injuries when struck by cars from behind. How does Newton's law of inertia apply here? How do headrests help to guard against this type of injury?
- Suppose you place a ball in the middle of a wagon that is at rest and then abruptly pull the wagon forward. Describe the motion of the ball relative to (a) the ground and (b) the wagon
- When a junked car is crushed into a compact cube, does its mass change? Its volume? its weight?
- If an elephant were chasing you, its enormous mass would be very threatening. But if you zigzagged, the elephant's mass would be to your advantage. Why?
- When you compress a sponge, which quantity changes: Mass, inertia, volume, or weight?
- A massive ball is suspended on a string ad slowly pulled by another string attached to it. (a) Is the string tension greater in the upper or the lower string? Which string is more likely to break? Which property, mass or weight, is important here? (b) If the string is instead snapped downward, which string is more likely to break? Is mass or weight important this time?
- skip
- A little girl hangs at rest from the ends of a rope placed above in a pulley (each one of her hands is holding on to one end of the rope). What is the tension in each rope she is holding?
- skip
- As Earth rotates about its axis, it takes three hours for the United States to pass beneath a point above Earth that is stationary relative to the sun, What is wrong with the following scheme? To travel from Washington, D.C. to San Francisco using very little fuel, simply ascend in a helicopter high over Washington, D.C. and wait three hours until San Francisco passes below.
- skip
- skip
- A medium-size American automobile has a weight of about 3000 pounds. What is its mass in kilograms?
- If a woman weight 500N on Earth, what would she weigh on Jupiter, where the acceleration of gravity is 26 m/s^2?
Newton's First Law of Motion- Inertia (Practice problems)
- At Earth's surface, g=9.8 m/s^2 (or roughly, 10 m/s^2)
- Weight = mass X acceleration due to gravity: W=mg
- Net force is the vector sum of all forces acting.
- Net force = 0 for an object in equilibrium
- What is the weight in newtons of Lily Lightweight, who has a mass of 40 kg?
- What is the weight in newtons of Lily's convertible, which has a mass of 1800 kg?
- What is the net force on a 1000-N barrel falling in air with an air drag of 400N?
- When a 1000-N barrel is sinking through the water at a constant speed, what is the upward force of the water on the barrel?
- What would be the weight of a gold crown on the moon if it has a mass of 3 kg? The acceleration due to gravity on the moon is 1/6 that on Earth.
- What is the mass of a 100-N crate of delicious candy?
- Larry Lightweight stands on a pair of bathroom scales. Each scale reads 300 N. What is Larry's mass?
- Suppose Larry stands with more weight on one scale than the other. If one scale reads 400 N, what does the other read?
- Just as a 1-kg ball sitting at the edge of a table falls off the edge, it is kicked horizontally with a force of 10 N. What is the net force on the ball during the kick?
- A high-flying jet cruises at an altitude of 30,000 feet at a constant velocity of 700 km/h. The force of the jet engines is 40,000 N. How much air drag acts on the craft?
Newton's Second Law of Motion (Review Questions)
- Distinguish between the relationship that defines acceleration and the relationship that states how it is produced?
- What is meant by the net force that acts on an object?
- Suppose a cart is being moved by a certain net force. If the net force is doubled, by how much does the cart's acceleration change?
- Suppose a cart is being moved by a certain net force. If a load is dumped into the cart so its mass is doubled, by how much does the acceleration change?
- Distinguish between the concepts directly proportional and inversely proportional. Support your statement with examples.
- State Newton's second law in words and then in the form of an equation.
- How much force does a 20,000 kg rocket develop to accelerate 1 m/s^2?
- What is the cause of friction, and in what direction does it act with respect to the motion of a sliding object?
- If the force of friction acting on a sliding crate is 100N, how much force must be applied to maintain a constant velocity? What will be the net force acting on the crate? What will be the acceleration?
- Distinguish between force and pressure
- Which produces more pressure on the ground, a person standing up or the same person lying down?
- The force of gravity is twice as great on a 2 kg rock as on a 1 kg rock. Why does the 2 kg rock not fall with twi e the acceleration?
- Why do a a coin and a feather in a vacuum tube fall with the same acceleration?
- Why do a coin and a feather fall with different accelerations in the presence of air?
- How much air resistance acts on a 100-N bag of nails that falls at its terminal speed?
- How do the air resistance and the weight of a falling object compare when terminal speed is reached?
- All other things being equal, why does a heavy sky diver have a terminal speed greater than a light sky diver? What can be done so that the terminal speeds are equal?
- What is the net force acting on a 25-N freely falling object? What is the net force when the object encounters 15N of air resistance? When it falls fast enough to encounter 25 N of air resistance?
- Calculate the acceleration of a 2000-kg, single engine airplane just before takeoff when the thrust of its engine is 500N.
- Calculate the acceleration of a 300,000-kg jumbo jet just before takeoff when the thrust for each of its four engines is 30,000N
- (a) Calculate the acceleration if you push with a 20=N horizontal force on a 2-kg block on a horizontal friction-free air table. (b) What occurs if the friction force is 4N?
- Calculate the horizontal force that must be applied to produce an acceleration of 1 g for a 1-kg puck on a horizontal friction-free air table.
- Calculate the horizontal force that must be applied to produce an acceleration of 1.8g for a 1.2kg puck on a horizontal friction-free air table.
- What is the difference between saying that one quantity if proportional to another and saying it is equal to another?
- If an object has no acceleration, can you conclude that no forces are exerted on it? Explain and draw a free-body diagram to illustrate an example.
- What is the acceleration of a rock at the top of its trajectory when thrown straight upward? Explain whether or not the answer is zero by using the equation a=F/m as a guide to your thinking.
- A rocket fired from its launching pad not only picks up speed, but its acceleration also increases significantly as firing continues. why is this so? (Hint: about 90% of the mass of a newly launched rocket is fuel)
- If you push horizontally on your book with a force of 1 N to make the book slide at constant velocity, how much is the force of friction on the book?
- When blocking in football, why does a defending lineman often attempt to get his body under that of his opponent and push upward? What effect does this have on the friction force between the opposing lineman's feet and the ground?
- Why does a sharp knife cut better than a dull knife?
- An aircraft gains speed during takeoff due to the constant thrust of its engines. When is the acceleration during takeoff greatest- at the beginning of the run along the runway or just before the aircraft lifts into the air? think, then explain.
- As a sky diver falls faster and faster through the air (before reaching terminal speed), does the net force on her increase, decrease, ,or remain unchanged? Does her acceleration increase, decrease, or remain unchanged? Defend your answers?
- After she jumps, a sky diver reaches terminal speed after 10 seconds. Does she gain more speed during the first second of fall or the ninth second of fall? Compared with the first second of fall, does she fall a greater or a lesser distance during the ninth second/
- A regular tennis ball and another one filled with sand are dropped at the same time from the top of a high building. Your friend says that even though air resistance is present, both balls should hit the ground at the same tie because they are the same size and "plow through" the same amount of air. What do you say?
- If a 1-N net force accelerates a 1-kg mass at 1m/s^2, what is the acceleration caused by a net force of 2N on a 2-kg mass?
- What is the acceleration of a 747 jumbo jet, mass 30,000 kg, i takeoff when the thrust for each of its four engines is 30,000N?
- A certain force applied to a 2-kg mass accelerates the mass at 3m/s^2. How much acceleration will the same force produce on a 4-kg mass?
- A horizontal force of 100N is required to push a crate across a factory floor at a constant speed. What is the net force acting on the crate? what is the force of friction acting on the crate?
- If a four-engine jet accelerates down the runway at 2 m/s^2 and one of the jet engines fails, how much acceleration will the other three produce?
- What will be the acceleration of a sky diver when air resistance is half the weight of the sky diver?
- If a loaded truck that can accelerate at 1 m/s^2 loses its load and has three-fourths of the original mass, what acceleration can it attain fro the same driving force?
- An occupant of a car has a chance of surviving a crash if the deceleration during the crash is not more than 30g. Calculate the force on a 70-kg person decelerating at this rate.
- skip
- skip
- When you drop two balls of different weights from the same height, you will see that for low speeds, they practically fall together. What happens if you let them roll together down the same inclined plane? If each is suspended from the same length string, made in, how much speed will the wagon pick up after Heather has pushed the wagon for 3to a pendulum, ad then displaced through the same angle, determine whether they swing back and forth in unison.
Newton's Second Law of Motion - Force and Acceleration (Practice Probs)
- The acceleration of an object is given by Newton's second law: a=F(net)/m
- Acceleration is in the same direction as the net force
- When air resistance is present, a falling object accelerates until air drag equals the weight- then the net force on it is zero and the acceleration is zero. It has reached terminal speed.
- The pressure P on an object is the applied force F divided by the area A over which the force acts P=F/A
- Calculate the acceleration of a 100-kg cart when the net force on it is 50N
- Calculate the horizontal force needed to make a 1-kg hockey puck accelerate at 1000 m/s^2
- What is the acceleration given to a 50-kg block of cement when it is pulled sideways with a net force of 800N?
- What is the pressure on a table when a 15-N dictionary with a 0.05 m^2 cover lies flat on it?
- Heather can apply a force of 72N to a wagon in which sits her little brother, Bryce. The combined mass of Bryce and the wagon is 48kg. If starting from rest, how much speed will the wagon pick up after Heather has pushed the wagon for 3s?
- When the wagon in the previous problem reaches a speed of 8 m/s, Heather lets go and Bryce puts on the brakes. If the wagon comes to rest 6s later, how much force did the brakes apply?
- A golf ball leaves the tee at a speed of 170 mph (75 m/s). If the ball has a mass of 0.05kg and gains this speed in 0.02x, what is the average force of impact of the club on the ball?
- A 500-kg subcompact car and a 1500kg standard car are given equal accelerations. How much greater is the force that acts on the more massive car?
- A astronaut of mass 90kg walks in space outside her spaceship and receives a 30-N force from a nitrogen spurt gun. (a) What acceleration does she experience? (b) If the duration of the spurt is 2 s, how fast will she be moving relative to the spaceship?
- A 2000-kg pickup truck is moving at a speed of 40 m/s as its brakes are applied, and comes to a stop in 10s. Assuming uniform acceleration, (a) what is the braking force applied to the truck? (b) how far does the truck travel while the brakes are applied?
- Scarlet Skydiver, who has a mass 60kg, jumps from a stationary helicopter. (a) What is the net force on her as she emerges fro the helicopter. (b) What is the net force on her 10s into the dive, when she has reached terminal speed? (c) What is her acceleration when she reaches terminal speed?
- Suppose Scarlet then opens her parachute. Air drag on the chute and Scarlet then becomes 2000N. (a) What is the net force on her now? (b) What is her acceleration?
- As Scarlet and the parachute slow down, the drag decreases until it equals Scarlet's weight. At that point, what is her acceleration? Will the new terminal speed be greater than, less than, or the same as the terminal speed before the parachute was opened?
- After being pushed and released, a 50-kg crate slides across a factory floor. Friction on the sliding crate is 200N. What is the crate's acceleration?
- What is the acceleration of a 20-kg container of paint pulled upward (not sideways) with a force of 300N?
- Skelly the child skater is propelled by rocket power Skelly and the rocket together have a mass of 25kg. When the thrusting force is 100N and friction is 20N, (a) what will be Skelly's acceleration? (b) How far will he go in 5s if he starts from rest?
- A firefighter of mass 80kg slides down a vertical pole with an acceleration of 4 m/s^2. What is the friction force that acts on the firefighter?
Newton's Third Law of Motion- Action & Reaction (Practice Problems)
- Force occurs when two objects interact. the interaction actually consists of two forces: each object exerts a force on the other. the two forces are equal in strength and opposite in direction
- When a force occurs, there are two objets and two forces; one force acts on each object
- What will be the acceleration of recoil when a 60-kg person on rollerblades pushes against a wall with a force of 30N?
- Two people attempt a tug-of-war on low-friction ice. One person has four times the mass of the other. Relative to the acceleration of the heavier person, what will be the acceleration of the lighter person?
- Two blocks, one three times as massive as the other, are connected by a compressed spring. When the spring is released, both blocks fly apart. Relative to the acceleration of the heavier block, what is the acceleration of the lighter block?
- What is the net force on a falling 1000N barrel hitting a pavement with 5000N of force?
- A boxer punches a sheet of paper in midair, and brings it from rest up to a speed of 40 m/s in 0.05s. If the mass of the paper is 0.01 kg, what force does the boxer exert on it?
- A 7-kg bowling ball moving at 6.0 m/s strikes a 1-kg bowling pin. If the ball slows to 4.5 m/s in 0.05s, how much force does it exert on the pin?
Newton's Third Law- Action & Reaction (Review Questions)
- In the interaction between a hammer and the nail it hits, is a force exerted on the nail? On the hammer? How many forces occur in this interaction?
- When a hammer exerts a force on a nail, how does the amount of force compare with that of the nail on the hammer?
- When you walk along a floor, what pushes you along?
- When swimming, you push the water backward- call this action. What is the reaction force?
- if the action is a bowstring acting on an arrow, identify the reaction force.
- When you jump up, the world really does recoil downward. Why can't this motion of the world be noticed?
- When a cannon is fired, how does the size of the force of the cannon on the cannonball compare with the force of the cannonball on the cannon? How does the acceleration of the cannon compare with that of the cannonball? Defend your answer.
- How can a rocket be propelled above the atmosphere where there is no air to "push against"?
- skip
- skip
- skip
- skip
- skip
- skip
- skip
- If you hit a wall with a force of 200N, how much force is exerted on you?
- Why can't you hit a feather in midair with a force of 200N?
- How does the saying "You get what you give" relate to Newton's Third Law?
- Your weight is the result of the gravitational force of Earth on your body. What is the corresponding reaction force?
- Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?
- Consider the two forces acting on a person who stands still, namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they comprise an action-reaction pair? Why or why not?
- If you walk on a log that is floating in the water, the log moves backward. Why?
- Why is it easier to walk on a carpeted floor than on a smooth, polished floor?
- If you step off a ledge, you accelerate noticeably toward Earth because of the gravitational interaction between you and Earth. Does Earth accelerate toward you as well? Explain?
- Suppose you're weighing yourself while standing next to the bathroom sink. Using the idea of action and reaction, explain why the scale reading will be less when you push down on the top of the sink. Why will the scale reading be more if you pull up on the bottom of the sink?
- When a high jumper leaves the ground, what is the source of the upward force that accelerates her? What force acts after her feet are no longer in contact with the ground?
- What is the reaction force to an action force of 1000N exerted by Earth on an orbiting communications satellite?
- If action equals reaction, why isn't Earth pulled into orbit around a communication satellite?
- if a bicycle and a massive truck have a head on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? defend your answer.
- A speeding bus makes contact with a bug that splatters onto the windshield. Because of the sudden force, the unfortunate bug undergoes a sudden deceleration. Is the corresponding force that the bug exerts against the windshield greater, less, or the same? Is the resulting deceleration of the bus greater than, less than, or the same as that of the bug?
- Some people used to think that a rocket could not travel to the moon because it would have no air to push against once it left Earth's atmosphere. We now know that idea was mistaken. What force propels a rocket when it is in a vacuum?
- Since the force that acts on a cannonball when a cannon is fired is equal and opposite to the force that acts on the cannon, does this imply a zero net force and therefore the impossibility of an accelerating cannonball? Explain
- Suppose you exert 200N on your refrigerator and push it across the kitchen floor at constant velocity. What friction force acts between the refrigerator and the floor? Is the friction force equal and opposite to your 200N push? Does the friction force make up the reaction force to your push?
- Your teacher challenges you and your best friend to each pull on a pair of scales attached to the ends of a horizontal rope, in tug-of-war fashion, so that the readings on the scales will differ. Can this be done? Explain.
- skip
- The strong man can withstand the tension force exerted by the two horses pulling in opposite directions. How would the tension compare if only one horse pulled and the left rope were tied to a tree? How would the tension compare if the two horses pulled in the same direction, with the left rope tied to the tree?
- A balloon floats motionless in the air. A balloonist begins climbing up the supporting cable. In which direction does the balloon move as the balloonist climbs? Explain.
- When you get up from a sitting position, do your feet push against the floor with a force equal to, more than, or less than your weight? Explain.
- When a weightlifter jerks a barbell over his head, is the force exerted on the barbell more than, less than, or equal to the barbell's weight? Explain.