# Work done by tension on cart

1. Feb 11, 2009

### TG3

1. The problem statement, all variables and given/known data
A cart of mass 5 kg is attached to a block of mass 3 kg by a string that passes over a frictionless pulley. The system is initially at rest and we will assume that friction can be ignored. The block falls a distance of 1 m.
What is the work done on the cart by the string during this fall?

2. Relevant equations
W= FD
W= Change in Kinetic Energy
K = mgh

3. The attempt at a solution

M=3
G=9.81
H=1
So 3 x 9.81 x 1= 29.43 J
But this answer is not correct. What am I doing wrong?

2. Feb 11, 2009

### tiny-tim

HI TG3!

You're saying that the work done on the cart is the change in KE of the cart, which is correct.

But you've used the mass of the block.

3. Feb 11, 2009

### TG3

Erm.... as opposed to what? I've tried the mass of the block, the mass of the cart, and the mass of both of them both put together x 9.81, and nothing works...

--Edit---
Never mind, I figured it out. g x ((m1xm2)/(m1+m2)).