Chapter 5

A horizontal force of 200 N is applied to a 55.0-kg cart across a 15.0-m level surface. If the cart accelerates at 2.0 m/s2, then what is the work done by the force of friction as it acts to retard the motion of the cart?

-1.4E+3 J

A 60-kg (including the passenger) sled is subject to a net force of 20 N pushing in the direction of the sled's motion as it is moving over a horizontal surface for a distance of 11 m after having started from rest. At this point the sled is released as it starts down a 10.0° incline. However, the snow is not very deep, and the sled stops after having moved an additional 35 m. What is the work done by friction while the sled is on the incline?

-3.8E+3 J

A horse pulls a 350-kg sled at constant speed along an icy road for a distance of 500 m. If the coefficient of kinetic friction between the sled and the road is 0.450, and the angle between the harness and the sled is 25°, what is the mechanical energy lost due to friction?

-6.4E+5 J

I use a rope 3.50 m long to swing a 10.8-kg weight around my head. The tension in the rope is 8.25 N. In half a revolution how much work is done by the rope on the weight?

0 J

A 2 500-kg ore car rolls 55.0 m down a frictionless 10.0° incline. If there is a horizontal spring at the end of the incline, what spring constant is required to stop the ore car in a distance of 2.10 m?

1.1E+5 kN/m

A 180-hp engine can deliver, in SI units, an average power of ____. (1 hp = 746 W)

1.3E+5 W

A Hooke's law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining double the kinetic energy received in the above situation?

1.41d

A force of 130 N is applied to a 50-kg mass in the direction of motion for a distance of 6.0 m and then the force is increased to 170 N for the next 4.0 m. For the 10 m of travel, how much work is done by the varying force?

1.5E+3 J

An airliner with mass 90 000 kg is flying at 900 km/h at a height of 15.0 km. What is its total energy (kinetic + potential) if the total was 0 when the airliner was at rest on the ground?

1.6E+10 J

Petra pushes a crate across a rough floor. A frictional force of 28.0 N acts to oppose the motion of the crate, and Petra pushes with a horizontal force of 36.4 N. If the net work Petra does is 94.5 J, through what distance did she push the crate?

11.3 m

A rock is thrown straight up with an initial velocity of 15.0 m/s. Ignore energy lost to air friction. How high will the rock rise?

11.5 m

An amount of work equal to 2.0 J is required to compress the spring in a spring-gun. What is the "launch speed" of a 26.0-g marble?

12.4 m/s

A girl and her bicycle have a total mass of 42 kg. At the top of the hill her speed is 4.00 m/s. The hill is 14.3 m high and 112 m long. If the force of friction as she rides down the hill is 20 N, what is her speed at the bottom?

13.8 m/s

A Hooke's law spring is compressed 14.6 cm from equilibrium, and the potential energy stored is 76.0 J. What compression (as measured from equilibrium) would result in 100 J being stored in this case?

16.7 cm

What is the kinetic energy of a 0.240-kg baseball thrown at 37.5 m/s?

169 J

Rupel pushes a box 7.00 m by applying a 25.0-N horizontal force. What work does she do?

175 J

A boat with mass 950 kg is heading into the harbor at a speed of 10.0 m/s. How much work is required to slow the boat to 1.0 m/s?

2.3E+4 J

Yuri, a Russian weightlifter, is able to lift 260 kg 2.10 m in 2.20 s. What is his power output?

2.43 kW

A 100-W light bulb is left on for 8.0 hours. Over this period of time, how much energy was used by the bulb?

2.9E+6 J

A 8.00-kg bowling ball falls from a 3.50-m shelf. Just before hitting the floor, what will be its kinetic energy? (g = 9.80 m/s2 and assume air resistance is negligible)

274 J

Old Faithful geyser in Yellowstone Park shoots water hourly to a height of 40.0 m. With what velocity does the water leave the ground?

28.0 m/s

Motor 1 does 30 J of work in 10 s, motor 2 does 2 J of work in 5 s, motor 3 does 7 J of work in 2 s, and motor 4 does 7 J of work in 3 s. List the motors in order of highest power produced to lowest power produced.

3, 1, 4, 2

Samantha pushes a 60-N crate up a ramp 30 m in length and inclined at 10° with the horizontal. What potential energy change does the crate experience?

3.1E+2 J

A 10.0-kg box starts at rest and slides 3.90 m down a ramp inclined at an angle of 10° with the horizontal. If there is no friction between the ramp surface and crate, what is the velocity of the crate at the bottom of the ramp? (g = 9.8 m/s2)

3.64 m/s

A 24.0-kg crate, initially at rest, slides down a ramp 4.0 m long and inclined at an angle of 20° with the horizontal. If there is no friction between ramp surface and crate, what is the kinetic energy of the crate at the bottom of the ramp? (g = 9.8 m/s2)

322 J

A professional skier reaches a speed of 58.0 m/s on a 30° ski slope. Ignoring friction, what was the minimum distance along the slope the skier would have had to travel, starting from rest?

343 m

By how much is the energy stored in a Hooke's law spring increased when its stretch is increased from 7.00 cm to 15.00 cm?

359%

A jet engine develops 1.50 × 105 N of thrust in moving an airplane forward at a speed of 900 km/h. What is the power developed by the engine?

37.5 MW

A baseball catcher puts on an exhibition by catching a 0.200-kg ball dropped from a helicopter at a height of 150 m above the catcher. If the catcher "gives" with the ball for a distance of 0.755 m while catching it, what average force is exerted on the mitt by the ball? (g = 9.80 m/s2)

389 N

A Hooke's law spring is mounted horizontally over a frictionless surface. The spring is then compressed a distance d and is used to launch a mass m along the frictionless surface. What compression of the spring would result in the mass attaining 4 times the speed received in the situation described here?

4.00d

A simple pendulum, 2.6 m in length, is released with a push when the support string is at an angle of 45.0° from the vertical. If the initial speed of the suspended mass is 1.25 m/s when at the release point, what is its speed at the bottom of the swing? (g = 9.8 m/s2)

4.1 m/s

A girl and her bicycle have a total mass of 46.0 kg. At the top of the hill her speed is 6.0 m/s, and her speed doubles as she rides down the hill. The hill is 15.0 m high and 105 m long. How much kinetic energy and potential energy is lost to friction?

4.3E+3 J

Preston pushes a wheelbarrow weighing 480 N to the top of a 45.0-m ramp, inclined at 22.0° with the horizontal, and leaves it. Tamara accidentally bumps the wheelbarrow. It slides back down the ramp, during which an 85.0-N frictional force acts on it over the 45.0 m. What is the wheelbarrow's kinetic energy at the bottom at of the ramp? (g = 9.8 m/s2)

4.3E+3 J

A 26.0-N crate starting at rest slides down a rough 4.8-m-long ramp, inclined at 21.0° with the horizontal. 18 J of energy is lost to friction. What will be the speed of the crate at the bottom of the incline?

4.49 m/s

A 1 000-kg sports car accelerates from zero to 25 m/s in 7.0 s. What is the average power delivered by the automobile engine?

4.5E+4 W

A baseball catcher puts on an exhibition by catching a 0.175-kg ball dropped from a helicopter at a height of 89.0 m. What is the speed of the ball just before it hits the catcher's glove 1.00 m above the ground? (g = 9.80 m/s2 and ignore air resistance)

41.5 m/s

A 35.0-N crate is pulled up a 4.0-m inclined plane by a worker at constant velocity. If the plane is inclined at an angle of 37° to the horizontal and there exists a constant frictional force of 25.0 N between the crate and the surface, what is the force applied by the worker?

46.1 N

A Hooke's law spring is compressed a distance d and is used to launch a particle of mass m vertically to a height h above its starting position. Under double the compression, the spring is now used to launch a particle of mass 2m. How high does the second mass rise above its starting position?

4h

A parachutist of mass 50.0 kg jumps out of an airplane at a height of 1 040 m. The parachute deploys, and she lands on the ground with a speed of 4.0 m /s. How much energy was lost to air friction during this jump?

5.1E+5 J

A pile driver drives a post into the ground. The mass of the pile driver is 2 600 kg and it is dropped through a height of 9.0 m on each stroke. If the resisting force of the ground is 4.0 × 106 N, how far is the post driven in on each stroke?

5.7E-2 cm

A speed boat requires 85.0 kW to move at a constant speed of 14.0 m/s. What is the resistive force of the water at this speed?

6 070 N

What is the minimum amount of energy required for a 60.0-kg climber carrying a 18-kg pack to climb Mt. Everest, 8 250 m high?

6.3E+6 J

Water flows over a section of Niagara Falls at a rate of 1.30 × 106 kg/s and falls 52.0 m. What is the power dissipated by the waterfall?

6.6E+8 W

A 62.0-kg woman runs up a flight of stairs having a rise of 4.28 m in a time of 4.20 s. What average power did she supply?

619 W

A Hooke's law spring is compressed 12.0 cm from equilibrium and the potential energy stored is 52.0 J. What is the spring constant in this case?

7 220 N/m

A 1 300-kg automobile moving at 21 m/s has the brakes applied with a deceleration of 3.0 m/s2. How far does the car travel before it stops?

7.4E+1 m

A golf ball hits a wall and bounces back at 3/4 the original speed. What part of the original kinetic energy of the ball did it lose in the collision?

7/16

A bobsled makes a run down an ice track starting at 250 m vertical distance up the hill. If there is no friction, what is the velocity at the bottom of the hill?

70.0 m/s

A pole vaulter clears 3.98 m. With what speed does he strike the mat in the landing area?

8.83 m/s

Adisa pulls a 35.0-N crate up a 4.00-m-long inclined plane at a constant velocity. If the plane is inclined at an angle of 39.0° to the horizontal and there is a constant force of friction of 13.0 N between the crate and the surface, what is the net change in potential energy of the crate?

88 J

A mover pushes a box of mass m = 56.0 kg along a horizontal floor a distance d = 2.50 m. The constant force exerted on the box by the mover makes an angle of 27.0° directed below the horizontal. Assume the floor is frictionless. If the work done by the mover is W = 200 J, what is the force exerted by the mover?

89.8 N

An automobile delivers 30.0 hp to its wheels when moving at a constant speed of 24.0 m/s. What is the resistance force on the automobile at this speed? (1 hp = 746 watts)

9.33E+2 N

The work done by static friction can be:

Any of the above.

A box is launched up a frictionless incline with an angle of elevation θ. The maximum height reached by the box is h. The box is again launched up the incline with the same initial speed it had before, but this time the angle of elevation has been increased to φ. How does the maximum height H reached this time by the box compare with the previous value h?

H = h

In a problem using energy considerations to solve for the speed of a ball thrown from the top of a building when it strikes the ground below, where should the potential energy have its zero value?

It doesn't matter since only differences in potential energy matter in solutions.

When a Hooke's law spring is stretched a distance 3x, how much is the increase in energy stored in it from when it was stretched a distance x? Give your answer in terms of a multiple of the energy stored in the spring when it is stretched a distance x.

It is 9 times as much.

When an object is dropped from a tower, what is the effect of the air resistance as it falls?

None of the above choices are valid.

Which of the following is not true about potential energy?

Potential energy has direction.

Three different-mass projectiles are launched from the top of a building each at different angles of elevation. Each particle has the same initial kinetic energy. Which particle has the greatest kinetic energy just as it impacts with the ground?

The one with the highest mass.

Two blocks are released from the top of a building. One falls straight down while the other slides down a smooth ramp. If all friction is ignored, which one is moving faster when it reaches the bottom?

They both will have the same speed.

As an object is lowered into a deep hole in the surface of the Earth, which of the following must be assumed in regard to its potential energy?

d. cannot tell from the information given

Which of the following is an example of a nonconservative force?

friction

A Hooke's law spring is compressed a distance d and is used to launch a mass m vertically to a height h above its starting position. Under the same compression d, the spring is now used to launch a mass of 2m. How high does this second mass rise?

h/2

A force of 5.0 N is applied to a 20-kg mass on a horizontal frictionless surface. As the speed of the mass increases at a constant acceleration, the power delivered to it by the force:

increases.

The unit of power, watt, is dimensionally the same as:

joule/second.

A spring with spring constant k is used to launch a mass m up a frictionless inclined plane having angle of elevation θ. What is the maximum height reached above the starting elevation of the mass during the motion of the mass if the spring is compressed a distance d before launch?

kd^2/2mg

The SI units for k, the spring constant, are equivalent to:

kg / s2.

Which of the following is that form of energy associated with an object's motion?

kinetic

Jasper takes two books of mass m1 and m2 off the floor and places them on a shelf at height h. The change in potential energy of the book with mass m1 is four times that of the book with mass m2. What is the relationship between m1 and m2?

m1 = 4m2

A pendulum consists of a mass m suspended from a string of length L. When the pendulum is swinging, how much greater is the mass's potential energy when the string is displaced from the vertical by the angle θ than when the mass is at the lowest position?

mgL(1 - cosθ)

A pendulum consists of a mass m suspended from a string of length L. When the pendulum is swinging, how much greater is the mass's potential energy when the string is displaced from the vertical by the angle θ than when the mass is at the lowest position?

mgL(1 - sinθ)

The unit of work, joule, is dimensionally the same as:

newton/second.

A suitcase is sitting on a horizontal conveyor belt, which is moving at speed v. The work done by the frictional force on the suitcase is

positive.

The rate at which work is done is equivalent to which of the following?

power

The area under the force vs. displacement curve represents:

work.

Is it possible for the total mechanical energy of a moving particle to be negative?

yes

A 1.00-kg ball has zero kinetic and potential energy. Ernie drops the ball into a 10.0-m-deep well. Just before the ball hits the bottom, the sum of its kinetic and potential energy is:

zero.

A 3.00-kg ball has zero potential and kinetic energy. Maria drops the ball into a 10.0-m-deep well. After the ball comes to a stop in the mud, the sum of its potential and kinetic energy is:

zero.

A hill is 150 m long and makes an angle of 12° with the horizontal. As a 60-kg jogger runs up the hill, how much work does gravity do on the jogger?

−1.83E+4 J