ACTIVITY: Kinetic and Potential Energy
EQ: What happens to an object’s kinetic and potential energy as it moves down a ramp?
BACKGROUND INFORMATION: The higher you lift an object, the more potential energy it has. Potential energy is stored
energy. The formula for potential energy is PE=mgh. When an object is dropped, potential energy converts to kinetic
energy. The faster an object moves, the greater its kinetic energy. The formula for kinetic energy is
.
RESULTS: A car is released from the top of a 0.54 m high track. The time the car goes through the photogate at different
positions along the track is measured. The following data is collected.
Table 1: Car height and photogate time data.
HEIGHT (M)
MASS OF CAR (kg)
PHOTOGATE TIME (s)
SPEED (m/s)
0.54
0.0558
None
0.48
0.0109
0.43
0.0079
0.37
0.0064
0.29
0.0049
0.23
0.0045
Calculate the speed at each position by dividing the width of the flag, 0.01 m, by the time.
Using the data above, complete table 2.
Table 2: Potential energy, kinetic energy, and total energy of a car moving down a .54 m high track.
HEIGHT (m)
POTENTIAL ENERGY (J)
KINETIC ENERGY (J)
TOTAL ENERGY (J)
0.54
0.48
0.43
0.37
0.29
0.23
To find PE, multiply the mass of the car by gravity and height.
Calculate KE by using the equation
.
Add PE and KE to find the total energy at that position.
THINKING ABOUT WHHAT YOU OBSERVED:
1. What happens to the car’s potential energy as it moves down the track? Why?
2. What happens to the car’s kinetic energy as it moves downhill? Why?
3. As the car moves downhill, does the total energy increase, decrease, or stay the same?
4. Where does the car have the most potential energy?
5. Where does the car have the most kinetic energy?