# Total Mechanical Energy Problem

1. Jan 15, 2012

### Snape1830

The 120 kg roller coaster just makes it to the top of hill A that is 15 m above the ground. It moves forward, picking up speed towards location B which is only 3 m above the ground. What is the total energy of the roller coaster as it passes location B, C, and D? Note: the velocity at the top of the hill is 0 m/s. The height of C= 8m and the height of D = 0 m. Ignore friction.

I know that total mechanical energy (TME) = PE + KE. However, I only have the velocity at the top of the hill and not at points B,C, and D. How do I find the velocity? I think I've done something like the Initial PE= final KE, but is that right? My teacher never told us that. Then further down on the questions it asks us to find the velocity of the roller coaster at these points, so is there a way to find TME without knowing the velocity? Do I use Work = change in kinetic energy?

Then another question asks us to find the kinetic energy at these points.

Last edited: Jan 15, 2012
2. Jan 15, 2012

### Staff: Mentor

Without friction, total mechanical energy is a conserved quantity. What's the total mechanical energy at location A?

3. Jan 15, 2012

### Snape1830

PE= mgh. So PE= 17640 J

Ohh I get it! So 17640=TME since kientic energy is 0 J. I completely forgot about that. Thanks!

4. Jan 15, 2012

### Staff: Mentor

You're welcome.