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Work Problems
1. A force of 800 N is needed to push a car across a lot. Two students push the car 40.0 m. How much work is
done?
2. How much work is done in lifting a 60.0 kg crate a vertical distance of 10.0 m?
3. A car has run out of gas. Fortunately, there is a gas station nearby. You must exert a force of 715 N on the car
in order to move it. By the time you reach the station, you have done 2.72 × 104 J of work. How far have you
pushed the car?
4. An applied force of 20 N accelerates a block across a level, frictionless surface from rest to a velocity of 8.0
m/s in a time of 2.5 s. Calculate the work done by this force.
5. A building under construction requires an amount of cement to be raised be lifted 76.2 m by a crane. If the
net work done on the cement is 1.31 × 103 J, what is the magnitude of the net force exerted on the cement?
6. A student librarian picks up a 0.95 kg book from the floor to a height of 1.25 m. She carries the book 8.0 m
to the shelves and places the book on a shelf that is 2.0 m high. How much work has been done on the book?
7. A force of 600 N is applied to a metal box to pull it 15.0 m across the floor. The rope used to pull is held at
an angle of 46 with the floor. How much work is done?
8. A gardener pushes down on the handle of a lawnmower at an angle of 45 with an applied force of 141 N,
while pushing the mower 8.5 m along level ground. Calculate the amount of work done.
Power Problems
1. A box that weighs 1000 N is lifted a distance of 20.0 m straight up by a rope and pulley system. The work is
done in 10.0 s. What is the power developed in kilowatts?
2. A rock climber wears a 12.0 kg knapsack while scaling a cliff. After 30.0 minutes, the climber is 8.2 m above
the starting point.
a. If the climber weighs 600 N, how much total work is done by the climber?
b. During the 30.0 min, what is the climber's average power in kilowatts?
3. An electric motor develops 65 kW of power as it lifts a loaded elevator 18.0 m in 40.0 s. How much force
does the motor deliver?
4. How long does it take a 2.5 kW electric motor to do 75,000 J of work?
5. A runner exerts a force of 334 N against the ground while using 2100 W of power. How long does it take the
runner to run a distance of 50.0 m?
Energy Problems
1. The 200 kg hammer of a pile driver is lifted 10.0 m. Find the gravitational potential energy of the system
when the hammer is at this height.
2. What is the speed of a 5.44 kg shot-put if its kinetic energy is 68 J?
3. A 50 kg cyclist on a 10 kg bicycle speeds up from 5.0 m/s to 10.0 m/s.
a. What is the total kinetic energy before accelerating?
b. What is the total kinetic energy after accelerating?
c. How much work was done to increase the kinetic energy of the cyclist?
d. Is it more work to speed up from 0 to 5.0 m/s than from 5.0 m/s to 10.0 m/s?
4. A steel ball has a mass of 4.0 kg and rolls along a smooth, level surface at 62 m/s.
a. Find its kinetic energy.
b. At first, the ball was at rest on the surface. A force acted on it through a distance of 22 m to give it
the speed of 62 m/s. What was the magnitude of the force?
Conservation of Energy
1. An 8.0 kg mass moves at 30.0 m/s.
a. What is its kinetic energy?
b. If the object is initially at rest, how much work was done on the object to give it this KE?
2. A 2.00 × 102 kg iceboat is propelled across the horizontal surface of a frozen lake by the wind. The wind
exerts a constant force of 4.00 × 102 N while the boat moves 0.90 km. Assume that frictional forces are
negligible and that the boat starts from rest. What is the boat’s final speed?
3. A hockey puck with an initial speed of 8.0 m/s coasts 45 m to a stop across the ice. If the force of friction on
the puck has a magnitude of 0.12 N, what is the puck’s mass?
4. A 450 kg compressor slides down a loading ramp that is 7.0 m long. Initially at rest, the compressor’s speed
at the bottom of the ramp is 1.1 m/s. What is the magnitude of the net force acting on the compressor?
5. A large chunk of ice with a mass of 15.0 kg falls from a roof 8.00 m above the ground.
a. What is the kinetic energy of the ice as it reaches the ground?
b. What is its speed as it reaches the ground?
6. A 15.0 kg object is moving with a velocity of +7.50 m/s. A force of -10.0 N acts on the object and its
velocity becomes 3.20 m/s. What is the displacement of the object while the force acts?
7. A block weighing 98.0 N falls 64.0 m.
a. What is the potential energy of the block at 64.0 m?
b. What speed does the block have as it strikes the ground?
8. During the hammer throw at a track meet, an 8.0 kg hammer is accidentally thrown straight up. If 784.0 J of
work were done on the hammer to give it vertical velocity, how high will it rise?
9. A partially filled bag of cement having a mass of 16.0 kg falls 40.0 m into a river from a bridge.
a. What is the kinetic energy of the bag as it hits the water?
b. Using energy considerations only, what vertical speed does it have on impact?
10. Some children go tobogganing on an icy hill. They start from rest at the top of the hill as show in t he
diagram. The toboggan and the children have a combined mass of 90 kg. If friction is small enough to be
ignored, determine:
a. the total mechanical energy of the toboggan at A.
b. the speed of the toboggan at B.
c. the speed of the toboggan at C.
Work problems
1. 32,000 J
2. 5880 J
3. 38 m
4. 200 J
5. 17.2 N
6. 18.62 J
7. 6,252 J
8. 847.5 J
Power Problems
1. 2 kW (2000 W)
2. I added the weight of the climber and the backpack together
a. 5884.32 J
b. 0.00327 kW (3.27 W)
3. 144,444 N
4. 30 s
5. 7.95 s
Energy Problems
1. 19,600 J
2. 5.3 m/s
3. I added the bike and the cycler to get 60 kg total weight
a. 750 J
b. 3,000 J
c. 2250 j
d. More work to go from 5-10 m/s
4. KE= and F=
a. 7688 J
b. 349.5 N
Conservation of Energy
1. KE=
a. 3600 J
b. 3600 J
2. 60 m/s
3. .184 kg
4. 38.9
5. PE=
a. 1176 J
b. 12.5 m/s
6. 34.51 m
7. PE=
a. 6272 J
b. 35.4 m/s
8. 10 m
9. KE =
a. 6272 J
b. 28 m/s
10. PE =
a. 8820 J
b. 14 m/s
c. 11.7m/s