Another work problem help!

1. Oct 6, 2012

NasuSama

Sorry for the second post, but I want to know how to solve such problem when it comes to this situation.

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

A vertical rope is used to lower a block of mass M = 48.3 kg at a constant acceleration of magnitude a = 1.54 m/s2. Find WT, the work done by the tension in the cord if the mass moves down distance s = 2.47 m.

2. Relevant equations

3. The attempt at a solution

Hm... Tried to use this form:

W = m(g - a)d

But I'm not sure if I'm at the right path.

2. Oct 6, 2012

cheahchungyin

It seems correct to me :)
m(g-a) is the force used to reduce the block acceleration.
then m(g-a)d is the work done..nothing else to be considered anymore from here

3. Oct 6, 2012

tiny-tim

Hi NasuSama!
No.

The definition of work done is W = F "dot" d
How did you get that equation? Did you use F = ma?

If so, your F is correct, your d is correct, but your "dot" isn't.

4. Oct 6, 2012

NasuSama

So W = F * d [Can't do the dot].

I used F = ma to get the equation. What about the answer? Is it correct. You said F is correct and d is correct, right?

My answer is around 987 J, but it's incorrect.

5. Oct 6, 2012

NasuSama

W = m(g - a) [dot] d doesn't seem quite right.

6. Oct 6, 2012

NasuSama

Never mind. I got the solution!