# Conservation of energy: Block pulled up frictionless plane

1. Feb 20, 2008

### nickclarson

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

A block of mass 3.16 kg, starting from rest, is pulled up a frictionless inclined plane that makes an angle θ = 27.1° with the horizontal by a string parallel to the plane. The tension in the string is 45.8 N. After travelling a distance 2.12 m, the speed of the block is 3.37 m/s. Find the work done by the tension force.

2. Relevant equations

$$U=mgh$$
$$W = KE_{f} - KE_{i}$$

3. The attempt at a solution

I came up with:

$$KE_{i} + U_{i} = KE_{f} + U_{f}$$
$$0 + 0 = KE_{f} - U_{f}$$

so since I am looking to find the final kinetic energy which is equal to work...

$$KE_{f} = -U_{f} = -mgh$$

but positive because W is positive.

I got the wrong answer though and I could be way off, could somebody point me on the right track?

Thanks,
Nick