# Solving problem dealing with PE + KE WITHOUT mass values?

1. Oct 26, 2012

### riseofphoenix

A group of students perform the same "Conservation of Mechanical Energy" experiment that you performed in lab by allowing a solid sphere and then a solid cylinder to roll down the ramp. The solid sphere was released from a height of 13.7 cm. From what height hcylinder should the solid cylinder be released so that it has the same speed as the solid sphere when it reaches the bottom of the ramp?

I just said "13.7 cm" but I got marked as "INCORRECT"

2. Oct 26, 2012

### bossman27

Hint: how is the moment of inertia of a cylinder different than that of a sphere?

3. Oct 26, 2012

### ehild

The initial potential energy at the top of the ramp transforms into kinetic energy at the bottom. The kinetic energy is the sum of the translational KE and the rotational one. The rotational energy depends of the moment of inertia, which depends on the shape.

ehild

4. Oct 26, 2012

### riseofphoenix

Wait what?
Can you put that in an equation?
I have no idea what you just said :(

5. Oct 26, 2012