Mastering Physics Sem 1 Review

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What is its mass?

1×10−15 kg

A car is skidding to a stop on a level stretch of road. Identify the number of the action/reaction pairs of forces between the car and the road surface.

2 pairs

What is its length?

2×10−6m

A football is kicked at an angle of 35 with a speed of 24 m/s. How far will the ball travel?

55 m

Suppose a plane accelerates from rest for 30 s, achieving a takeoff speed of 80 m/s after traveling a distance of 1200 m down the runway. A smaller plane with the same acceleration has a takeoff speed of 56 m/s. Starting from rest, after what distance will this smaller plane reach its takeoff speed?

588m

At t=5.0s, which car has traveled the furthest?

Betty

A car coasts at a constant speed over a circular hill. Which of the free-body diagrams in the figure is correct?

C - the normal force is less than the weight

Your car is skidding to a stop from a high speed. Identify all forces acting on the object.

Drag, Weight, Normal, Kinetic Friction

Suppose your efforts work, and the car begins to move forward out of the mud. As it does so, the force of the car on the rope is

Equal to the force of the rope on the car.

Which car has the largest acceleration?

Goes from 0 m/s to 3.8 m/s in 1.0 s

Jonathan accelerates away from a stop sign. His eight-year-old daughter sits in the passenger seat. On whom does the back of the seat exert a greater force?

Jonathan

A mountain climber is hanging from a vertical rope, far above the ground and far from the rock face. The rope is vertical. Identify the forces on the mountain climber.

Tension, Weight

Use Newton's laws to explain why you seem to be "thrown forward" as the car stops. Is there really a force pushing you forward?

The net force on you has remained zero because the net vertical force is zero and there are no horizontal forces. According to Newton's first law, if the net force on you is zero, then you continue to move in a straight line with a constant velocity. That is what happens to you when the car slows down. You continue to move forward with a constant velocity.

Choose the appropriate explanation how such a low value is possible given Saturn's large mass - 100 times that of Earth.

This low value is possible because the density of Saturn is so low.

A falcon is hovering above the ground, then suddenly pulls in its wings and begins to fall toward the ground. Air resistance is not negligible. Identify the forces on the falcon.

Weight, Drag

A skydiver has his parachute open and is floating downward through the air at a constant speed. Identify all the forces acting on the system skydiver-parachute.

Weight, Drag

Currently, the moon goes around the earth once every 27.3 days. If the moon could be brought into a new circular orbit with a smaller radius, its orbital period would be

less than 27.3 days.

Two football players are pushing a 60 kg blocking sled across the field at a constant speed of 2.0 m/s. The coefficient of kinetic friction between the grass and the sled is 0.30. Once they stop pushing, how far will the sled slide before coming to rest?

0.68 m

When you blink your eye, the upper lid goes from rest with your eye open to completely covering your eye in a time of 0.024 s. What is your upper eyelid's final speed as it hits the bottom eyelid?

0.84m/s

When you blink your eye, the upper lid goes from rest with your eye open to completely covering your eye in a time of 0.024 s. Estimate the distance that the top lid of your eye moves during a blink.

1 cm

What is the length of its DNA, in millimeters?

1 mm

A girl stands on a sofa. Identify the number of the action/reaction pairs of forces between the girl and the sofa.

1 pair

Some car manufacturers claim that their vehicles could climb a slope of 44. For this to be possible, what must be the minimum coefficient of static friction between the vehicle's tires and the road?

1.0

Weddell seals make holes in sea ice so that they can swim down to forage on the ocean floor below. Measurements for one seal showed that it dived straight down from such an opening, reaching a depth of 0.30 km in a time of 5.0 min. What was the speed of the diving seal?

1.0 m/s

A rectangle has length 3.24 mm and height 0.432 mm . To the correct number of significant figures, what is its area?

1.40 m2

The earth formed 4.57×109 years ago. What is this time in seconds?

1.44×1017s

Estimate the average speed, in m/s, with which the hair on your head grows. Make this estimate from your own experience noting, for instance, how often you cut your hair and how much you trim.

10−8m/s

110 min

A car drives horizontally off a 75-m-high cliff at a speed of 29 m/s. Ignore air resistance. How far from the base of the cliff will the car hit?

110m

A person walks briskly at 2.10 m/s . How much time will it take them to walk one mile?

12.8 min

Suppose you and a friend, each of mass 60 kg , go to the park and get on a 4.5-m-diameter merry-go-round. You stand on the outside edge of the merry-go-round, while your friend pushes so that it rotates once every 6.5 seconds. What is the magnitude of the (apparent) outward force that you feel?

130 N

A ball thrown at an initial angle of 37.0 and initial velocity vi = 24.0 m/s reaches a maximum height h, as shown in With what initial speed must a ball be thrown straight up to reach the same maximum height?

14.4 m/s

A car can go from 0 to 60 mph in 14 s . A second car is capable of twice the acceleration of the first car. Assuming that it could maintain the same acceleration at higher speeds, how much time will this second car take to go from 0 to 120mph?

14s

A car can go from 0 to 60 mph in 8.0 s . Assuming that it could maintain the same acceleration at higher speeds, how long would it take the car to go from 0 to 120 mph?

16 s

Riders on a Ferris wheel move in a circle with a speed of 4.50 m/s. As they go around, they experience a centripetal acceleration of 2.40 m/s2. What is the diameter of this particular Ferris wheel?

16.9 m

A cannon, elevated at 40∘∘ is fired at a wall 300 m away on level ground, as shown in the figure below. The initial speed of the cannonball is 89 m/s. At what height h does the ball hit the wall?

160m

1700 m/s

On the earth, an astronaut throws a ball straight upward; it stays in the air for a total time of 3.1 s before reaching the ground again. If a ball were to be thrown upward with the same initial speed on the moon, how much time would pass before it hit the ground?

19s

In the winter sport of curling, players give a 20 kg stone a push across a sheet of ice. The stone moves approximately 40 m before coming to rest. The final position of the stone, in principle, only depends on the initial speed at which it is launched and the force of friction between the ice and the stone, but team members can use brooms to sweep the ice in front of the stone to adjust its speed and trajectory a bit; they must do this without touching the stone. Judicious sweeping can lengthen the travel of the stone by 3 m. Suppose that the stone is launched with a speed of 3 m/s and travels 40 m before coming to rest. What is the approximate magnitude of the friction force on the stone?

2 N

If the organism were to move along a straight path, how many meters would it travel in one day?

2 m

A student walks 1.6 mi west and then 1.6 mi north.

2.3 mi

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions. Suppose the designers of the water slide want to adjust the height above the water so that riders land twice as far away from the bottom of the slide. What would be the necessary height above the water?

2.4 m

Suppose one night the radius of the earth doubled but its mass stayed the same. What would be an approximate new value for the free-fall acceleration at the surface of the earth?

2.5m/s2

A newly discovered planet has twice the mass and three times the radius of the earth. What is the free-fall acceleration at its surface, in terms of the free-fall acceleration g at the surface of the earth?

2/9g

While standing in a low tunnel, you raise your arms and push against the ceiling with a force of 200 N. Your mass is 80 kg. What force does the ceiling exert on you?

200 N

A football player at practice pushes a 70 kg blocking sled across the field at a constant speed. The coefficient of kinetic friction between the grass and the sled is 0.30. How much force must he apply to the sled?

210N

The cylindrical space station in (Figure 1), d = 250 m in diameter, rotates in order to provide artificial gravity of g for the occupants. How much time does the station take to complete one rotation?

22s

A truck is traveling at 30 m/s on a slippery road. The driver slams on the brakes and the truck starts to skid. If the coefficient of kinetic friction between the tires and the road is 0.20, how far will the truck skid before stopping?

230 m

A 6.0 kg block has an acceleration of 0.40 m/s2 when a force is exerted on it. A second block has an acceleration of 0.10 m/s2 when subject to the same force. What is the mass of the second block?

24 kg

A bird flies 3.6 km due west and then 2.1 km due north. Another bird flies 2.1 km due west and 3.6 km due north.

Two cylindrical space stations, the second four times the diameter of the first, rotate so as to provide the same amount of artificial gravity. If the first station makes one rotation in the time T, then the second station makes one rotation in what time?

A 3.0 kg puck slides due east on a horizontal frictionless surface at a constant speed of 4.5 m/s . Then a force of magnitude 6.0 N , directed due north, is applied for 1.5 s . What is the northward component of the puck's velocity?

3.0 m/s

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions. What is the vertical component of the velocity of a rider as he or she hits the water?

3.4 m/s

When you blink your eye, the upper lid goes from rest with your eye open to completely covering your eye in a time of 0.024 s. What is the acceleration of your eyelid? Assume it to be constant.

3.5×101m/s2

If an astronaut can jump straight up to a height of 0.6 m on earth, how high could he jump on the moon?

3.6 m

Compute 3.24 mm + 0.432 mm to the correct number of significant figures.

3.67 m

A car drives horizontally off a 75-m-high cliff at a speed of 29 m/s. Ignore air resistance. How long will it take the car to hit the ground?

3.9 s

Wings on race cars push them into the track. The increased normal force makes large friction forces possible. At one Formula One racetrack, cars turn around a half-circle with diameter 190 m at 68 m/s. For a 610 kg vehicle, the approximate minimum static friction force to complete this turn is

30000 N

A 2.5 kg ball is suspended by two light strings as shown in What is the tension T in the angled string?

32 N

In the winter sport of curling, players give a 20 kg stone a push across a sheet of ice. The stone moves approximately 40 m before coming to rest. The final position of the stone, in principle, only depends on the initial speed at which it is launched and the force of friction between the ice and the stone, but team members can use brooms to sweep the ice in front of the stone to adjust its speed and trajectory a bit; they must do this without touching the stone. Judicious sweeping can lengthen the travel of the stone by 3 m. A curler pushes a stone to a speed of 3.0 m/s over a time of 1.6 s. Ignoring the force of friction, how much force must the curler apply to the stone to bring it up to speed?

38 N

A 4.5 kg dog sits on the floor of an elevator that is accelerating downward at 1.20 m/s2. What is the magnitude of the force of the dog on the elevator floor?

39 N

A 4.5 kg dog sits on the floor of an elevator that is accelerating downward at 1.20 m/s2. What is the magnitude of the normal force of the elevator floor on the dog?

39 N

A football is kicked at an angle of 40 with a speed of 24 m/s. To the nearest second, how long will the ball stay in the air?

A cannon, elevated at 40∘∘ is fired at a wall 300 m away on level ground, as shown in the figure below. The initial speed of the cannonball is 89 m/s. How long does it take for the ball to hit the wall?

4.4s

A bird flies 3.8 km due west and then 2.4 km due north.

4.5 km

A ball on a string moves around a complete circle, once a second, on a frictionless, horizontal table. The tension in the string is measured to be 10 N. What would the tension be if the ball went around in only half a second?

40 N

Motor neurons in mammals transmit signals from the brain to skeletal muscles at approximately 25 m/sm/s. Estimate how much time in ms (10−3s) it will take for a signal to get from your brain to your hand.

40 ms

If you kick a football, at what angle to the ground should you kick the ball for the maximum range - that is, the greatest distance down the field?

Blades of grass grow from the bottom, so, as growth occurs, the top of the blade moves upward. During the summer, when your lawn is growing quickly, estimate this speed, in m/s. Make this estimate from your experience noting, for instance, how often you mow the lawn and what length you trim.

4×10−8m/s

A 3.0 kg puck slides due east on a horizontal frictionless surface at a constant speed of 4.5 m/s . Then a force of magnitude 6.0 N , directed due north, is applied for 1.5 s . What is the speed of the puck?

5.4 m/s

An object's average density ρ is defined as the ratio of its mass to its volume: ρ=M/V. The earth's mass is 5.94×10+24kg, and its volume is 1.08×10+12km3. What is the earth's average density?

5.50×103kg/m3

Eric has a mass of 70 kg. He is standing on a scale in an elevator that is accelerating downward at 1.7 m/s2. What is the approximate reading on the scale?

570 N

Formula One race cars are capable of remarkable accelerations when speeding up, slowing down, and turning corners. At one track, cars round a corner that is a segment of a circle of radius 95 m at a speed of 68 m/s. What is the approximate magnitude of the centripetal acceleration, in units of g?

The images of trees in the figure come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn't steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years. At the end of year 3, a rope is tied to the very top of the tree to steady it. This rope is staked into the ground 15 feet away from the tree. What angle does the rope make with the ground?

On the earth, an astronaut can safely jump to the ground from a height of 1.3 m ; her velocity when reaching the ground is slow enough to not cause injury. From what height could the astronaut safely jump to the ground on the moon?

7.8 m

A car is traveling at vx = 24 m/s. The driver applies the brakes and the car decelerates at ax = -4.0 m/s2. What is the stopping distance?

72 m

The images of trees in the figure come from a catalog advertising fast-growing trees. If we mark the position of the top of the tree in the successive years, as shown in the graph in the figure, we obtain a motion diagram much like ones we have seen for other kinds of motion. The motion isn't steady, of course. In some months the tree grows rapidly; in other months, quite slowly. We can see, though, that the average speed of growth is fairly constant for the first few years. What is the tree's speed of growth, in feet per year, from t=1yrt=1yr to t=3yrt=3yr?

9 ft/yr

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions. At the end of the first section of the motion, riders are moving at what approximate speed?

9 m/s

The two block in (Figure 1) are at rest on frictionless surfaces. What must be the mass of the right block in order that the two blocks remain stationary? Suppose that m = 16 kg.

9.7 kg

At what angle to the ground should you kick the ball for the maximum "hang time" - that is, the maximum time in the air?

While standing in a low tunnel, you raise your arms and push against the ceiling with a force of 200 N. Your mass is 80 kg. What force does the floor exert on you?

980 N

9×10−8m/s

Choose an example of a vertical motion with a negative velocity and a negative acceleration.

A ball dropped from a height during its downward motion.

Choose an example of a vertical motion with a positive velocity and a negative acceleration.

A ball thrown upward, before it starts to fall back down.

shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 0.40 kg. Explain your reasoning.

A larger slope implies a smaller mass. We know the mass of object 2, and we can find the other masses relative to m2 by comparing their slopes.

During which segments, if any, does the bacterium have the same displacement?

AB and CD

During which segments, if any, does the bacterium have the same velocity?

AB and CD

The gas pedal in a car is sometimes referred to as "the accelerator." Which other controls on the vehicle can be used to produce acceleration?

All of the above

During which segments, if any, does the bacterium have the same speed?

All paths

Suppose you are an astronaut in deep space, far from any source of gravity. You have two objects that look identical, but one has a large mass and the other a small mass. How can you tell the difference between the two?

Assuming you can exert a reproducible force in throwing both objects, you could throw each and note the acceleration each obtains.

Suppose a spacecraft orbits the moon in a very low, circular orbit, just a few hundred meters above the lunar surface. The moon has a diameter of 3500 km, and the free-fall acceleration at the surface is 1.60 m/s2. The material that comprises the side of the moon facing the earth is actually slightly more dense than the material on the far side. When the spacecraft is above a more dense area of the surface, the moon's gravitational force on the craft is a bit stronger. In order to stay in a circular orbit of constant height and speed, the spacecraft could fire its rockets while passing over the denser area. The rockets should be fired so as to generate a force on the craft

Away from the surface of the moon.

Which combination of the vectors shown in (Figure 1) has the largest magnitude?

B +A −C

Which of the three drag racers had the greatest acceleration at t=0 s?

Betty

The figure below shows block A sitting on top of block B. A constant force F is exerted on block B, causing block B to accelerate to the right. Block A rides on block B without slipping.

Block B exerts a friction force on block A, directed to the right.

Dave pushes his four-year-old son Thomas across the snow on a sled. As Dave pushes, Thomas speeds up. Which statement is true?

Both forces have the same magnitude.

In the winter sport of curling, players give a 20 kg stone a push across a sheet of ice. The stone moves approximately 40 m before coming to rest. The final position of the stone, in principle, only depends on the initial speed at which it is launched and the force of friction between the ice and the stone, but team members can use brooms to sweep the ice in front of the stone to adjust its speed and trajectory a bit; they must do this without touching the stone. Judicious sweeping can lengthen the travel of the stone by 3 m. The sweepers in a curling competition adjust the trajectory of the stone by

Decreasing the coefficient of friction between the stone and the ice.

Tennis balls experience a large drag force. A tennis ball is hit so that it goes up and then comes back straight down. The direction of the drag force is

Down and then up. Submit

A person gives a box a shove so that it slides up a ramp, then reverses its motion and slides down. The direction of the force of friction is

Down the ramp and then up the ramp.

Assume that you are pulling on the rope but the car is not moving. What is the approximate direction of the force of the mud on the car?

East

When you are pulling on the rope as shown, what is the approximate direction of the tension force on the tree?

East

Three arrows are shot horizontally. They have left the bow and are traveling parallel to the ground as shown in the figure. Air resistance is negligible. (Figure 1) Rank in order, from largest to smallest, the magnitudes of the horizontal forces F1, F2, and F3 acting on the arrows. Some may be equal. State your reasoning.

F1=F2=F3=0 because there is no change in the horizontal motion of the arrows.

A Porsche challenges a Honda to a 400 mm race. Because the Porsche's acceleration of 3.4 m/s2 is larger than the Honda's 3.0 m/s2, the Honda gets a 110 mm head start - it is only 290 mm from the finish line. Assume, somewhat unrealistically, that both cars can maintain these accelerations the entire distance. Who wins the race?

Honda wins. (by 1.4)

Normally, jet engines push air out the back of the engine, resulting in forward thrust, but commercial aircraft often have thrust reversers that can change the direction of the ejected air, sending it forward. When might these thrust reversers be useful in practice?

If the ejected air is directed downward, the thrust force is up. Jets can take off vertically without needing a runway this way. If the ejected air is directed forward then thrust force is backward. This might be desirable to slow the plane down.

If the ejected air is directed forward then thrust force is backward (Newton's 3rd law).

You are standing on a straight stretch of road and watching the motion of a bicycle; you choose your position as the origin. At one instant, the position of the bicycle is negative and its velocity is positive. Is the bicycle getting closer to you or farther away? Explain.

If the position of the bicycle is negative it is to your left. The bicycle's velocity is positive, or to the right, so the bicycle is getting closer to you.

If you are standing still, the upward normal force on you from the floor is equal in magnitude to the weight force that acts on you. But it's possible to move so that the normal force is greater than your weight. Explain how this could be done.

If you jump up, during the initial phase when you are still in contact with the floor, you are accelerating upward. This means the net force on you must be upward, so the upward normal force must be bigger than the downward weight force.

Why is it impossible for an astronaut inside an orbiting space station to go from one end to the other by walking normally?

In an orbiting station, after one foot pushes off there isn't a force to bring the astronaut back to the "floor" for the next step.

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions. Suppose the acceleration during the second section of the motion is too large to be comfortable for riders. What change could be made to decrease the acceleration during this section?

Increase the radius of the circular segment.

You've slammed on the brakes and your car is skidding to a stop while going down a 20 degree hill. Identify all the forces acting on the car.

Kinetic Friction, Normal, Weight

A spring-loaded gun shoots a plastic ball. The trigger has just been pulled and the ball is starting to move down the barrel. The barrel is horizontal. Identify all the forces acting on the ball.

Kinetic Friction, Spring, Normal, Weight

You are going sledding with your friends, sliding down a snowy hill. Friction can't be ignored. Riding solo on your sled, you have a certain acceleration. Would the acceleration change if you let a friend ride with you, increasing the mass?

No, increasing the mass does increase the net force on the system, but it also increases the inertia. a=Fnet/m. Since both the net force and mass are increased they still cancel, leaving the acceleration the same.

A stubborn 140 kg pig sits down and refuses to move. To drag the pig to the barn, the exasperated farmer ties a rope around the pig and pulls with his maximum force of 800 N. The coefficients of friction between the pig and the ground are μs=0.80 and μk=0.50. Is the farmer able to move the pig?

No, the farmer will not be able to budge the pig, because the maximum static friction force is greater than the farmer's maximum pull of 800 N

The rope can support a maximum tension of 6100 NN . Is this rope strong enough to do the job? Choose the correct answer and explanation.

No. The tension in the ropes exceeds the maximum value, the ropes will break.

A skier is sliding down a 15∘∘ slope. Friction is not negligible. Identify the forces on the skier.

Normal, Kinetic Friction, Weight

A basketball player is getting ready to jump, pushing off the ground and accelerating upward. Identify all the forces acting on the basketball player.

Normal, Weight

If a car stops suddenly, you feel "thrown forward." We'd like to understand what happens to the passengers as a car stops. Imagine yourself sitting on a very slippery bench inside a car. This bench has no friction, no seat back, and there's nothing for you to hold on to. Identify all of the forces acting on you as the car slowing down.

Normal, Weight

A jet plane is speeding down the runway during takeoff. Air resistance is not negligible. Identify the forces on the jet.

Normal, Weight, Thrust, Drag

Which combination points directly to the left?

Q −P

Two planets orbit a star. You can ignore the gravitational interactions between the planets. Planet 1 has orbital radius r1 and planet 2 has r2=4r1. Planet 1 orbits with period T1. Planet 2 orbits with period

T2=8T1

Josh and Taylor, standing face-to-face on frictionless ice, push off each other, causing each to slide backward. Josh is much bigger than Taylor. After the push, which of the two is moving faster?

Taylor will be moving faster.

A box is being dragged across the floor at a constant speed by a rope pulling horizontally on it. Friction is not negligible. Identify all the forces acting on the box.

Tension, Normal, Weight, Kinetic Friction

In (Figure 1), at the instant shown, is the apparent weight of the car's driver greater than, less than, or equal to his true weight? The car is on top of the hill.

The apparent weight of the car's driver is less than his true weight.

A car travels along a straight east-west road. A coordinate system is established on the road, with xx increasing to the east. The car ends up 16 mi west of the origin, which is defined as the intersection with Mulberry Road. If the car's displacement was -27 mi , what side of Mulberry Road did the car start on? How far from the intersection was the car at the start?

The car started 11 mi east of Mulberry Road.

In the winter sport of curling, players give a 20 kg stone a push across a sheet of ice. The stone moves approximately 40 m before coming to rest. The final position of the stone, in principle, only depends on the initial speed at which it is launched and the force of friction between the ice and the stone, but team members can use brooms to sweep the ice in front of the stone to adjust its speed and trajectory a bit; they must do this without touching the stone. Judicious sweeping can lengthen the travel of the stone by 3 m. Suppose the stone's mass is increased to 40 kg, but it is launched at the same 3 m/s. Which one of the following is true?

The force of friction would now be greater.

Here's a great everyday use of the physics described in this chapter. If you are trying to get ketchup out of the bottle, the best way to do it is to turn the bottle upside down and give the bottle a sharp upward smack, forcing the bottle rapidly upward. (Figure 1) Think about what subsequently happens to the ketchup, which is initially at rest, and use Newton's first law to explain why this technique is so successful.

The inertia of the ketchup will keep it from moving if it isn't too tightly adhered to the sides of the moving bottle.

You are cycling around a circular track at a constant speed. Does the magnitude of your acceleration change? The direction?

The magnitude of the acceleration doesn't change. But the direction does.

A man's higher initial acceleration means that a man can outrun a horse over a very short race. A simple - but plausible - model for a sprint by a man and a horse uses the following assumptions: The man accelerates at 6.0 m/s2 for 1.8 s and then runs at a constant speed. A horse accelerates at a more modest 5.0 m/s2 but continues accelerating for 4.8 s and then continues at a constant speed. A man and a horse are competing in a 200 m race. The man is given a 100 m head start, so he begins 100 mm from the finish line. Who wins the race?

The man wins the race.

A beach ball is thrown straight up, and some time later it lands on the sand. Is the magnitude of the net force on the ball greatest when it is going up or when it is on the way down? Or is it the same in both cases? Explain. Air resistance should not be neglected for a large, light object.

The only contact force is the force of air drag on the ball. The only long-range force is the weight of the ball. Drag always points in the direction opposite to the motion. Thus the weight of the ball and the drag force always reinforce each other if the ball is moving straight up. The net force is larger on the way up.

An astronaut takes his bathroom scale to the moon and then stands on it. Is the reading of the scale his true weight? Select the correct explanantion.

The reading on the moon will be the moon-weight, or the gravitational force of the moon on the astronaut. This would be about 1/6 of the astronaut's earth-weight or the gravitational force of the earth on the astronaut (while standing on the scales on the earth).

A rider on a water slide goes through three different kinds of motion, as illustrated in the figure. Use the data and details from the figure to answer the following questions. During which section of the motion is the magnitude of the acceleration experienced by a rider the greatest?

The second.

A ball on a string moves in a vertical circle as shown in (Figure 1). When the ball is at its lowest point, is the tension in the string greater than, less than, or equal to the ball's weight?

The tension in the string is greater than the ball's weight.

The tire on this drag racer is severely twisted: The force of the road on the tire is quite large (most likely several times the weight of the car) and is directed forward as shown in (Figure 1) Is the car speeding up or slowing down? Explain

The way the tire is twisted indicates that the force of the road on the tire is forward. Since this force is likely greater than the backward air resistance force, the net force is also forward; therefore, the car is accelerating in the forward direction.

The wood block in the figure below is at rest on a wood ramp. (Figure 1) In which direction is the static friction force on block 1?

There's not enough information to tell.

A student at the top of a building of height h throws ball A straight upward with speed v0 and throws ball B straight downward with the same initial speed. Compare the ball's accelerations, both direction and magnitude, immediately after they leave her hand. Is one acceleration larger than the other? Or are the magnitudes equal?

They are equal.

A student at the top of a building of height h throws ball A straight upward with speed v0 and throws ball B straight downward with the same initial speed. Compare the final speeds of the balls as they reach the ground.

They are equal.

Scallops eject water from their shells to provide a thrust force. (Figure 1) shows a smoothed graph of actual data for the initial motion of a 25 g scallop speeding up to escape a predator. How does this force compare to the 0.25 N weight of the scallop?

This force is 1/10 of the weight of the scallop.

The sum of the three forces acting on the center point of the rope is assumed to be zero because

This point is not accelerating.

Toward the center of the moon.

Weight, Normal

You are driving on the highway, and you come to a steep downhill section. As you roll down the hill, you take your foot off the gas pedal. You can ignore friction, but you can't ignore air resistance. Identify all the forces acting on the car.

Weight, Normal, Drag

A baseball player is sliding into second base. Identify the forces on the baseball player

Weight, Normal, Kinetic Friction

A bag of groceries is on the back seat of your car as you stop for a stop light. The bag does not slide. Identify all the forces acting on the

Weight, Normal, Static Friction

A sprinter has just started a race and is speeding up as she runs down the track. The sprinter is running to the right. Identify all the forces acting on the sprinter.

Weight, Normal, Static Friction

An ascending elevator, hanging from a cable, is coming to a stop. Identify all forces acting on the elevator from the list below.

Weight, Tension

An elevator, suspended by a single cable, has just left the tenth floor and is speeding up as it descends toward the ground floor. Neglect the friction. Identify all the forces acting on the elevator.

Weight, Tension

You look up from your textbook and observe a spider, motionless above you, suspended from a strand of spider silk attached to the ceiling. You distract yourself by identifying the forces acting on the spider. What are they?

Weight, Tension

(Figure 1) shows a situation in which the force of the road on the car's tire points forward. In other situations, the force points backward. Give an example of such a situation.

When the car is going forward and slowing down.

An airplane has been directed to fly in a clockwise circle, as seen from above, at constant speed until another plane has landed. When the plane is going north, is it accelerating?

Yes, it is. Since the plane is moving in a circle and constantly changing direction, at any point along its motion the plane is constantly accelerating.

In 1780, in what is now referred to as "Brady's Leap," Captain Sam Brady of the U.S. Continental Army escaped certain death from his enemies by running over the edge of the cliff above Ohio's Cuyahoga River in (Figure 1), which is confined at that spot to a gorge. He landed safely on the far side of the river. It was reported that he leapt 22 ft (≈6.7 m) across while falling 20 ft (≈ 6.1 m). The world-record time for the 100 m dash is approximately 10 s. Given this, is it reasonable to expect Brady to be able to run fast enough to achieve Brady's leap?

Yes, the obtained speed is less than the world-record.

Suppose that, while in a squatting position, you stand on your hands, and then you pull up on your feet with a great deal of force. You are applying a large force to the bottoms of your feet, but no matter how strong you are, you will never be able to lift yourself off the ground. Use your understanding of force and motion to explain why this is not possible.

You can't lift yourself off the floor because the net external force on you is still zero.

If a car stops suddenly, you feel "thrown forward." We'd like to understand what happens to the passengers as a car stops. Imagine yourself sitting on a very slippery bench inside a car. This bench has no friction, no seat back, and there's nothing for you to hold on to. Describe what happens to you as the car slows down.

You continue to move forward with the initial speed of the car.

You are walking up an icy slope. Suddenly your feet slip, and you start to slide backward. Will you slide at a constant speed, or will you accelerate?

You will accelerate because the kinetic friction is less than the maximum static friction.

A block has acceleration a when pulled by a string. If two identical blocks are glued together and pulled with twice the original force, what will their acceleration be?

A 77 kg man weighs himself at the north pole and at the equator. Which scale reading is higher?

at the north pole

Dana has a sports medal suspended by a long ribbon from her rearview mirror. As she accelerates onto the highway, she notices that the medal is hanging at an angle of 11 from the vertical. Does the medal lean toward or away from the windshield?

away from the windshield

Which of the quantities are zero throughout the flight?

A ball is thrown straight up into the air. At each of the following instants, is the ball's acceleration ay equal to g, −g, 0, <g, or >g? At the very top (maximum height)?

ay=−g

A ball is thrown straight up into the air. At each of the following instants, is the ball's acceleration ay equal to g, −g, 0, <g, or >g? Just after leaving your hand?

ay=−g

A ball is thrown straight up into the air. At each of the following instants, is the ball's acceleration ay equal to g, −g, 0, <g, or >g? Just before hitting the ground?

ay=−g

Walking without slipping requires a static friction force between your feet (or footwear) and the floor. As described in this chapter, the force on your foot as you push off the floor is forward while the force exerted by your foot on the floor is backward. But what about your other foot, the one moved during a stride? What is the direction of the force on that foot as it comes in contact with the floor?

backward

Give an example of a trip you might take in your car for which the distance traveled as measured on your car's odometer is not equal to the displacement between your initial and final positions.

circular motion with a constant speed

Small-plane pilots regularly compete in "message drop" competitions, dropping heavy weights (for which air resistance can be ignored) from their low-flying planes and scoring points for having the weights land close to a target. A plane 65 m above the ground is flying directly toward a target at 46 m/s . The pilot looks down at the weight after she drops it. Where is the plane located at the instant the weight hits the ground?

directly over the target

In an amusement-park ride, cars rolling along at high speed suddenly head up a long, straight ramp. They roll up the ramp, reverse direction at the highest point, then roll backward back down the ramp. Which way does their acceleration vector point as the cars roll back down the ramp?

downward along the ramp

Scallops use jet propulsion to move from one place to another. Their shells make them denser than water, so they normally rest on the ocean floor. If a scallop wishes to remain stationary, hovering a fixed distance above the ocean floor, it must eject water _____ so that the thrust force on the scallop is _____.

downward, upward

An airplane has been directed to fly in a clockwise circle, as seen from above, at constant speed until another plane has landed. When the plane is going north, in what direction does the acceleration vector point?

east

How fast (in km/h) must a plane fly along the earth's equator so that the sun stands still relative to the passengers? The radius of the Earth is 6400 km. In which direction must the plane fly, east to west or west to east?

east to west

The radius of Jupiter is 11 times that of earth, and the free-fall acceleration near its surface is 2.5 times that on earth. If we someday put a spacecraft in low Jupiter orbit, its orbital speed will be

greater than that for an earth satellite.

A person is pushing horizontally on a box with a constant force, causing it to slide across the floor with a constant speed. If the person suddenly stops pushing on the box, the box will

immediately begin slowing down and eventually stop.

A group of students is making model cars that will be propelled by model rocket engines. These engines provide a nearly constant thrust force. The cars are light-most of the weight comes from the rocket engine-and friction and drag are very small. As the engine fires, it uses fuel, so it is much lighter at the end of the run than at the start. A student ignites the engine in a car, and the car accelerates. As the fuel burns and the car continues to speed up, the magnitude of the acceleration will

increase

The velocity at instant 1 is _________ and the velocity at instant 2 is _________.

negative, negative

Alyssa pushes to the right on a filing cabinet; the friction force from the floor pushes on it to the left. Because the cabinet doesn't move, these forces have the same magnitude. Do they form an action/reaction pair?

Shannon decides to check the accuracy of her speedometer. She adjusts her speed to read exactly 70 mph on her speedometer and holds this steady, measuring the time between successive mile markers separated by exactly 1.00 mile. If she measures a time of 47 ss , is her speedometer accurate?

Suppose two vectors have unequal magnitudes. Can their sum be 0?

Your forehead can withstand a force of about 6.0 kN before fracturing, while your cheekbone can only withstand about 1.3 kN. Are you in danger of a fracture if the ball hits you in the forehead?

You throw a rock upward. The rock is moving upward, but it is slowing down. If we define the ground as the origin, the position of the rock is _____ and the velocity of the rock is _____.

positive, positive

A sports car is advertised as capable of "reaching 60 mph in 5 seconds flat, cornering at 0.85g, and stopping from 70 mph in only 168 feet." In which of those three situations is the magnitude of the car's acceleration the smallest?

reaching 60 mph in 5 seconds flat

In uniform circular motion, which of the following quantities are constant?

speed, magnitude of net force

What is the force that is holding the box up, the force that is opposite the weight force?

static friction force

A 1.0 kg wood block is pressed against a vertical wood wall by a 12 N force as shown in the figure. (Use μs= 0.5 for wood on wood.) If the block is initially at rest, will it move upward, move downward, or stay at rest?

stay at rest

stopping from 70 mph in only 168 feet

The floor is frictionless. Block 1 is on top of Block 2, with a pulley system connected on the left of the blocks. There is a force pulling block 2 to the right. On block 2?

to the left

The floor is frictionless. Block 1 is on top of Block 2, with a pulley system connected on the left of the blocks. There is a force pulling block 2 to the right. In which direction is the kinetic friction force on block 1 in the figure?

to the right

too low

A Thompson's gazelle can reach a speed of 13 m/s in 3.0 s . A lion can reach a speed of 9.5 m/s in 1.0 s . A trout can reach a speed of 2.8 m/s in 0.12 s .

trout

At the lowest point of the circle the ball has reached its maximum speed. What is the direction of the force her hand exerts on the ball at this point?

upward

For a projectile, which of the following quantities are constant during the flight: x, y, vx, vy, v, ax, ay?

vx, ax, ay

A tennis player hits a ball 2.0 m above the ground. The ball leaves his racquet with a speed of 20 m/s at an angle 5.0 above the horizontal. The horizontal distance to the net is 7.0 m, and the net is 1.0 m high. Does the ball clear the net?

yes

Your forehead can withstand a force of about 6.0 kN before fracturing, while your cheekbone can only withstand about 1.3 kN. Are you in danger of a fracture if the ball hits you in the cheek?

yes

Find the rider's acceleration vector at the highest position of the motion diagram in

Δv =v4−v3

Use a similar analysis to find the rider's acceleration vector at the leftmost position of the motion diagram in.

Δv =v7−v6

Find the rider's acceleration vector at the lowest position of the motion diagram in (Figure 3)

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