Chapter 3 Mechanical Energy Worksheet
Kinetic Energy: E k 
1 2
mv
2
Remember: mass must be in kg, velocity must be in m/s
1. Barry Bonds swings a bat which has a mass of 1500 g at a velocity of 55 m/s. How
many joules of kinetic energy could he give to a ball? (2269 J)
2. Calculate the Ek of a car which has a mass of 1000 kg and is moving at the rate of
100 km/h. (385000 J)
3. You serve a volleyball with a mass of 2.1 kg. After 1 second in the air, the ball has 10
Joules of kinetic energy. What is the speed of the ball at this point? (3 m/s)
Potential Energy: E p  mgh
(g=9.8N/kg)
Mass must be in kg, and height must be
in m.
4. Calculate the potential energy of a 150g bird that is sitting on a 20m platform. (29.4
J)
5. A 3kg medicine ball has a potential energy of 150J. How high above the floor is the
medicine ball being held? (5.1 m)
Mechanical Energy: E m  E p  E k
and E m1 E m 2
so.. E p1 E k 1 E p 2  E k 2
Note: For these problems we are ignoring air resistance and friction.
6. A 0.750 kg ball is dropped from rest at a point 0.80 m above the floor. There is no
air resistance, and the floor is at zero potential energy. Find the mechanical energy at
the highest point, and the velocity of the ball when it reaches the floor. (6J, 4 m/s)
7. During a flood a tree truck of mass 100 kg falls down a waterfall. The
waterfall is 5 m high. Calculate..
a) the potential energy of the tree trunk at the top of the waterfall. (4900 J)
b) the kinetic energy of the tree trunk at the bottom of the waterfall. (4900 J)
c) the magnitude of the velocity of the tree trunk at the bottom of the waterfall.
(9.9m/s)
8. A tennis ball, of mass 120 g, is dropped from a height of 5 m.
a) What is the potential energy of the ball when it has fallen 3 m? (2.35 J)
b) What is the velocity of the ball when it hits the ground? (9.9 m/s)
9. A skier, mass 50 kg, is at the top of a 6.4 m ski slope.
a) Determine the maximum velocity that she can reach when she skies to the
bottom of the slope. (11.2 m/s)
10. A truck of mass 1.2 tons is parked at the top of a hill, 150 m high. The truck driver
lets the truck run freely down the hill to the bottom.
a) What is the maximum velocity that the truck can achieve at the bottom of the hill?
(54.2 m/s)