Video Lab: Kinematics Answers

1. What is the average initial speed of the popper?
The maximum height of the popper averages to 1.81m. You may have a slightly different average maximum height. The speed at the top of the trajectory is 0 m/s. Use the 4th kinematic equation to find the initial speed:
v² = v_o² + 2gΔy
0 = v_o² + 2(-9.8)(1.81)
v_o = 6.0 m/s

2. How would the maximum height change if the the experiment was performed on the moon? Explain your answer. (Clue: the value of "g" on the moon is 6 times less that that on Earth.)
If the experiment was performed on the moon (g = 9.8/6 = 1.6 m/s²) the average maximum height would be greater than 1.81 m. The lower magnitude of the acceleration would allow the popper to rise to over 11 m before stopping. Wouldn't you like to play basketball on the moon? Dunking the ball would be easy for almost everyone!
0 = (6.0)² + 2(-1.6)(Δy)
Δy = 11.3 m
Additionally, since there is no atmosphere on the moon, the popper would rise even higher due to the lack of air resistance.

3. What is the speed of the popper when it is 1.0 m below its maximum height?
The popper will drop from its maximum height, where it has no speed, due to gravitational acceleration. Use the 4th kinematic equation to find the speed 1.0 m below maximum height.
v² = v_o² +2gΔy
v² = 0 - 19.6(-1.0)
v = 4.4 m/s (this is the magnitude of the velocity)

4. What is the speed of the popper when it hits the floor on the way back down?
The popper will have the same speed when it returns to surface level as it had when leaving the surface on the way up.
v = 6.0 m/s