# Homework Question. Need Help If Possible.

1. Oct 9, 2004

### Physicist7

I have a question that I must answer, and am finding it difficult to get. It is probably easy, my brain is just not functioning. It is higshchool phsyics question. Anyways how to get the answer and any advice would be great. Thanks!

Question: Suppose a stone of mass 350 g is thrown straight up from the ground with kinetic energy of 9.8 J (EK= 9.8J). How high will it rise before it starts to come down again?

2. Oct 9, 2004

### arildno

At the top, you have only potential energy, no kinetic energy.
Since mechanical energy is conserved, what does this imply that the height must be?

3. Oct 9, 2004

### Physicist7

So does this mean we can use Eg=mgh. m= 0.35 kg g=9.8 Eg= 9.8 J , and so h= Eg/mg. Since kinetic energy is converted to potential energy, and energy is always conserved then potential energy is also 9.8 J?

4. Oct 9, 2004

### arildno

Precisely!
(When there is no kinetic energy present, of course..)

5. Oct 9, 2004

### Physicist7

Hey arildno,

Thanks a lot I appreciate it. I did something like that at first but not with the idea of law of conservation in mind, and so it did not make any sense. However, now it does. Thanks again! Take Care.

6. Oct 9, 2004

### Physicist7

So the final answer is 2.85 m. Correct?