Question

A pole vaulter runs forward, plants his pole, rises in the air and lands. What point represents his greatest amount of gravitational potential energy?
A) when he initially lands

B) as he runs forward to plant the pole

C) just before he starts to fall to the ground

D) after take-off as the pole expands and lifts the vaulter toward the bar

Answer 1

C) Just before he starts to fall to the ground Remember that "gravitational potential energy" is the energy the object potentially has if it were to drop from the current height. So let's look at the options and see what's correct. A) When he initially lands * He's currently near the lowest height. So his gravitational potential energy is quite low. So this is the wrong choice. B) As he runs forward to plant the pole * He's on the ground. So has almost no height. So almost no gravitational potential energy. So this too is wrong. C) Just before he starts to fall to the ground * Ah. He's at his maximum height. So his potential gravitational potential energy is maximized. This is the correct choice. D) After take-off as the pole expands and lifts the vaulter toward the bar * He's at a low height. So once again, this is a bad choice.

Answer 2

Answer:

C)  just before he starts to fall to the ground

Explanation:

The maximum amount of gravitational potential energy is when the vaulter is at the highest position in the air, just as before he starts to fall to the ground. There is potential energy when he plants the pole, but that is converted to kinetic energy as it lifts him upward.