Question

Which describes the relationship between potential and kinetic energy of a ball thrown up in the air as it falls back to the ground?

A.
Kinetic energy increases; gravitational potential energy decreases.

B.
Kinetic energy equals gravitational potential energy.

C.
The mass of the ball is required to answer this.

D.
Gravitational potential energy increases; kinetic energy increases.

Answer 1

@theEric

Answer 2

@PsiSquared

Answer 3

Do you have any thoughts or guesses?

Answer 4

either A or D

Answer 5

Okay, so we've narrowed it down, hopefully it is one of those.

Lets think about each. Which one do you want to look at first?

Answer 6

top to bottom so A

Answer 7

but can u quickly explain it i have to go in like 3 min

Answer 8

i also have 1 more what are the answers

Answer 9

@theEric

Answer 10

Sorry! Okay, so, you know what those energies are, right? Kinetic energy is always related to what?

Answer 11

movement?

Answer 12

Right! Higher speed, more energy. As a ball falls, it gets faster. So it has more kinetic energy. That part of (A) is correct.

Now the potential energy. What is it related to?

Answer 13

It is the distance left to fall [to a chosen reference, usually the ground].

Answer 14

So, as the ball falls, what happens to this distance?

The formula for PE is \({\rm PE}=mgh\) where \(g\approx9.8\rm\ m/s\).

Answer 15

ok...

Answer 16

So, the ball falls. What happens to its height?

Answer 17

The ball's height decreases, and thus so does the PE.

This make sense, since the gravitational potential energy is the energy that you have the potential to gain from gravitational force.

Answer 18

So is it A?? If the ball is dropping, wouldn't that imply that the gravitational potential energy is decreasing, making the kinetic energy increase??

Answer 19

Yep! :)