Question

Read through the scenarios below and calculate the predicted change in kinetic energy of the object compared to a
50 kg ball traveling at 10 m/s.

A 50 kg ball traveling at 20 m/s would have
kinetic energy.

A 50 kg ball traveling at 5 m/s would have
kinetic energy.

A 50 kg person falling at 10 m/s would have
kinetic energy.

Answer 1

First compute the baseline (50 kg at 10 m/s):
KE = 1/2 m v^2 = 0.5·50·10^2 = 25·100 = 2,500 J.

Now each scenario (and change relative to 2,500 J):

1) 50 kg ball at 20 m/s:
KE = 0.5·50·20^2 = 25·400 = 10,000 J.
Change = 10,000 − 2,500 = +7,500 J (four times the baseline).

2) 50 kg ball at 5 m/s:
KE = 0.5·50·5^2 = 25·25 = 625 J.
Change = 625 − 2,500 = −1,875 J (one quarter of the baseline).

3) 50 kg person falling at 10 m/s:
KE = 0.5·50·10^2 = 2,500 J.
Change = 2,500 − 2,500 = 0 J (same as the baseline — KE depends only on mass and speed).