Conservation of Energy Calculations
Use the kinetic and potential energy formula, as well as the Law of
Conservation of Energy, to solve the following problems.
EP = mgh
EK = ½ mv2
The Law of Conservation of Energy states that energy cannot be created or
destroyed but can be converted from one type of energy to another.
Ep lost = EK gained
OR
EK lost = EP gained
Assume g = 9.80ms-2 on Earth for these calculations.
1. A strongman at a circus lifts a 100kg barbell above his head to a
height of 1.80m.
a) What is the potential energy of the barbell?
b) If the strongman dropped the barbell, what would its kinetic energy
be just before it hit the ground?
2. A rollercoaster car, mass 200kg, is propelled up to the highest point
of its journey, 40.0m above ground level.
a) What is the maximum velocity the rollercoaster could reach as it
descends?
b) At what height above ground level would this occur?
3. A ball, with mass 500g, is dropped from a balcony. The ball hits the
ground with a velocity of 8.85ms-1. How high is the balcony?
4. A yo-yo, with mass 100g, has a string length of 50.0cm. Find the
maximum speed of the yo-yo when it is dropped, assuming that the
string is tied to a child’s finger.
5. A child on a swing, with a combined mass of 32.0kg, swings through
its lowest point with a speed of 4.00ms-1. Calculate the maximum
height the child will swing to.
6. An air rocket, mass 0.150kg, is launched vertically with an initial
velocity of 25ms-1. At the point where it’s upward velocity has
decreased to 15ms-1, calculate the:
a) Kinetic energy
b) Potential energy
ANSWERS
1. a) 1764J
b) 1764J
2. a) 28ms-1
b) 0m (just as it reaches ground level)
3. 4.00m
4. 3.13ms-1
5. 0.816m
6. a) 16.9J
b) 30.0J