# Homework Help: Conservation of energy help

1. Jan 27, 2005

### bls555

okay, there is a roller coaster with 2 hills.. this is what I know:
1st hill height: 40m
2nd hill height: 25m
mass of coaster: 500kg
I was asked to find out the PE at top of hill #1, I did that and got 196,000J
Now I have to findthe KE at the bottom of hill #1, as well as finding the velocity at various spots, how do I do this?
Thanks a LOT for the help in advance.

2. Jan 27, 2005

### JFo

Make a list of the values for the PE and KE of the system at each point you want to evaluate. (make sure you set up an appropriate diagram,, from your first answer I assume your x axis lies along the ground)

Then make use of the equation for conservation of mechanical energy

KE_intial + PE_initial = KE_final + PE_final

do you know the equations for KE and PE?

Last edited: Jan 27, 2005
3. Jan 28, 2005

### bls555

PE = mgh
KE = 1/2mv²

I don't get how I'm supposed to find KE without knowing velocity, or without knowing T to find velocity (V = d/t).
EDIT: Yeah, each hill starts and ends at ground level, sorry for not including that.

Last edited: Jan 28, 2005
4. Jan 28, 2005

### mtong

At the bottom of hill one the KE will equal the PE at the top of hill one. One you get that you can calculate the velocity by solving Ek=1/2mv^2 using the mass of the coaster and KE that you just found.

This is of course assuming no losses

5. Jan 28, 2005

Thank you!