# Change in gravitational potential energy and work done against gravity

1. Apr 8, 2009

### Amber3046

1. The problem statement, all variables and given/known data
a 46.0kg child cycles up a large hill to a point that is vertical distance of 5.25m above the starting position find:
a.) The change in the childs gravitational potential energy
b.) The amount of work done by the child against gravity

2. Relevant equations
delta Eg=mg delta h?
W=delta Eg-g?

3. The attempt at a solution
delta Eg=(46.0kg)(9.80m/s2)(5.25m)
delta Eg=2366.7 J {This number seems too high though, and it wouldn't be the change. I don't know how to get that}
W=2366.7-9.80
W=2356.9J
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Apr 8, 2009

### Thaakisfox

The first part is ok, that is the change..

But for the second part, are you sure can do that??
Check the units..., you are subtracting joules from m/s^2

3. Apr 8, 2009

### Amber3046

I don't know if you can do that. It was just my guess, do you know how to do that?

4. Apr 8, 2009

### tnutty

what is the formula for the amount of work done thats given in your book. Write all of them

5. Apr 8, 2009

### Thaakisfox

Well of course you cant do that. What was your line of thought that got you there? Maybe we can clear it up then ;)

6. Apr 8, 2009

### Amber3046

My line of thought was that I would take the Gravitational Potential Energy and subtract the acceleration of gravity (9.81m/s^2). I don't think that it's right, that was just something I tried.