# Work and Energy of a mass

1. Nov 2, 2008

### Eternal Sky

1. The problem statement, all variables and given/known data

Problem: Two objects of different mass start from rest, are pulled by the same magnitude net force, and are moved through the same distance. The work done on object A is 500 J. After the force has pulled each object, object A moves twice as fast as object B. (a) How much work is done on object B? (b) What is the kinetic energy of object A after being pulled? (c) What is the kinetic energy of object B after being pulled?

2. Relevant equations

$W_n_e_t = \frac{1}{2}mv_2^2 - \frac{1}{2}mv_1^2$

3. The attempt at a solution

I believe that the answer to part (a) is 500 J also, since both objects are pulled through the same distance by the same force. I attempted to solve part (b) by using the above equation, but since I don't know the mass or the velocity, it didn't work out.

If someone could help me, I would greatly appreciate it.

2. Nov 2, 2008

### tiny-tim

Hi Eternal Sky!

ah … the whole point of the work-energy theorem … ∆W = ∆KE … is that you don't need to know how to calculate KE …

(so you don't even need the whole of that equation of yours )

you just calculate ∆W, and ∆KE is automatically the same!!

3. Nov 2, 2008

### Eternal Sky

Ah, I see. Thanks a lot for your help!