# Conservation of Energy

1. Oct 21, 2013

### KTiaam

1. The problem statement, all variables and given/known data

A mass m = 2 is in free fall. The acceleration of gravity is g = 10. All numbers are in mks units. The position y(t) and velocity v(t) of the mass as a function of time t are y(t)=9−5t2 and v(t)=−10t. Find each of the energies (K,U,E) as a function of time t. Hint: substitute v(t) into K(v), substitute y(t) into U(y).

2. Relevant equations

k = 1/2mv2
u = mgy

3. The attempt at a solution

I know that:
Work = ΔK
-ΔU = ΔK

im having trouble switching the equation to a function of time.
Am i trying to approach the problem in the wrong way?

any help is appreciated. Thanks!

Last edited: Oct 21, 2013
2. Oct 21, 2013

### MuIotaTau

Your formula for $U$ is a little off. (Hint: check your units!)

3. Oct 21, 2013

### KTiaam

oh okay i solved the problem thank you!

4. Oct 21, 2013

### MuIotaTau

Sure thing, happy to help!