# Work problem

1. Feb 29, 2008

[SOLVED] Work problem

A vertical rope is used to lower a mass 44.9 kg at a constant acceleration of magnitude 4.57 m/s2. Find the work done by the tension in the cord if the mass moves down distance 2.66 m.

W = F (change in X)

First, I tried to get the tension by:

-T + mg = ma
- T = ma - mg
T = -ma + mg
T = - (4.57 m/s^2)(44.9 kg) + (44.9 kg) (9.81 m/s^2)
T = 235.276 N

W = T (change of x)
W = 235.276 N (2.66 m) = 625.83416

However this seems to be wrong so my second attempt

T -mg = ma
T = ma + mg
T = 645.662 N

W = T (change of x)
W = 645.662 N (2.66 m) = 1717.46092

It seems I'm doing something wrong or overlooking a vital piece of information, I was wondering if someone could point me in the right direction.

2. Feb 29, 2008

The first attempt looks good to me, except that the work done would be negative.

3. Feb 29, 2008

### Dick

I can't find anything wrong with your first attempt. It looks correct. The second attempt IS wrong. It would be right if mass were accelerating 4.57m/sec^2 in an upwards direction. But it doesn't look like that's what the question is asking. Have you tried just changing the number of significant figures in the answer?

4. Feb 29, 2008