# Homework Help: Potential Energy problem help

1. Oct 17, 2012

### Larrytsai

If I have a mass m1 sitting on an incline plane attached by a rope and a pulley to another mass m2 hanging off the incline plane, what would be the potential energy?

I was thinking that m1 only plays a role on the potential energy.

2. Oct 17, 2012

### SammyS

Staff Emeritus
Can m2 also rise and/or fall ?

3. Oct 17, 2012

### Larrytsai

m2 can rise or fall

4. Oct 17, 2012

### SammyS

Staff Emeritus
In that case, its potential energy changes.

Is m2 part of the system ?

5. Oct 17, 2012

### Larrytsai

yes m2 is conneced by a rope and I would like to find the velocity of m1 after it leaves the ramp.

So if it does change the systems potential energy would it just be

PE = g*(m1*height + m2*height)

the height of each respective mass are different.

6. Oct 17, 2012

### SammyS

Staff Emeritus
Yes, the height of each respective mass is different. All that matters is change in height. Mass, m1, is on an inclined plane, so when the height of m2 decreases by Δh, the height of m1 increases by a lesser amount. Use trig to relate the two.

7. Feb 18, 2013

### QuantumJock

Potential energy will not affected by the other mass.

PE = mgh , mass x gravity x height.

You know the mass, and you know gravity is equal to 9.81 so you will need to know the height.

Jock

8. Feb 18, 2013

### SammyS

Staff Emeritus
Hello QuantumJock. Welcome to PF !

You have replied to a thread which has been idle for several months .

9. Feb 18, 2013

### QuantumJock

Oh woops I'm sorry! Still new!

Jock