Physics I 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 2.50-kg projectile is launched at an angle of 20.0° above the horizontal with an initial speed of 100 m/s from the top of a building 40 m high. If the projectile is traveling 85.0 m/s at its maximum height of 47.0 m, how much work has been done on the projectile by air friction?

-3.3E+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

I drop a 55-g golf ball from 2.50 m high. It rebounds to 1.65 m. How much energy is lost?

0.46 J

A boat with mass of 1 200 kg is traveling at 12 m/s. What is the magnitude of the force required to stop the boat if it undergoes a displacement of 85 m?

1 000 N

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

A 6.1-g bullet has a velocity of 475 m/s when it penetrates a wooden door to a depth of 3.5 cm. Assuming the frictional force that stops the bullet is constant, how long does it take from the time the bullet hits the door till it comes to a stop?

1.5E-4 s

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

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

A simple pendulum, 1.00 m in length, is released from rest when the support string is at an angle of 48.0° from the vertical. What is the speed of the suspended mass at the bottom of the swing? (g = 9.80 m/s2 and ignore air resistance)

2.55 m/s

If both mass and velocity of a ball are tripled, the kinetic energy is increased by a factor of:

27.

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 simple pendulum, 2.0 m in length, is released by a push when the support string is at an angle of 25° from the vertical. If the initial speed of the suspended mass is 1.6 m/s when at the release point, to what maximum angle will it move in the second half of its swing?

32.8°

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 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 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

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 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

An Olympic skier moving at 19.5 m/s down a 17.0° slope encounters a region of wet snow, of coefficient of friction μk = 0.740. How far down the slope does she go before stopping?

46.7 m

The net force acting on a 4.92-kg object is given by Fx = (10 − x) N, where Fx is in newtons and x is in meters. How much work is done on the object as it moves from x = 0 to x = 12.4 m?

47.1 J

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

The force acting on an object is given by Fx = (5x - 10) N, where x is in meters. What is the net work done by the force as the object moves from x = 0 to x = 4.50?

5.6 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?

7 200 N/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 worker pushes a sled with a force of 38.0 N over a level distance of 3.60 m. If a frictional force of 16.0 N acts on the wheelbarrow in a direction opposite to that of the worker, what net work is done on the wheelbarrow?

79.2 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

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

If during a given physical process the only force acting on an object is friction, which of the following must be assumed in regard to the object's kinetic energy?

It cannot be determined from the information given.

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.

A student has to work the following problem: A block is being pulled along at constant speed on a horizontal surface a distance d by a rope supplying a force F at an angle of elevation q. The surface has a frictional force acting during this motion. How much work was done by friction during this motion? The student calculates the value to be -Fdsinq. How does this value compare to the correct value?

The answer cannot be found until it is known whether q is greater than, less than, or equal to 45°.

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?

decrease

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?

kd2/2mg

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 box slides across a floor and comes to rest. The work done by the frictional force on the box is

negative.

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.

Which of the following is that form of energy associated with an object's location in a conservative force field?

potential

The quantity of work equal to one joule is also equivalent to which of the following?

watt ⋅ s

A very light cart holding a 100-N box is moved at constant velocity across a 10-m level surface. What is the net work done in the process?

zero

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 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

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:

−294 J.