# Easy Energy Q

1. May 11, 2010

### bon

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

A railway wagon runs on frictionless rails and is pulled by an engine travelling at
10 ms−1 . The wagon is loaded at constant rate with 1000 kg of coal, dropped vertically
from rest for a time of 2 s. What is the work done by the engine to keep the wagon
moving at constant speed? Is the work done equal to the kinetic energy imparted to
the coal and, if not, explain why not.

2. Relevant equations

3. The attempt at a solution

So the work done is 50,000J right?

My hench is that this is not exactly equal to the KE imparted to the coal...but im not sure how to explain this...something to do with downward impulse of coal on wagon?

Thanks

2. May 12, 2010

### bon

anyone?

3. May 12, 2010

### diazona

How did you get 50,000J?

4. May 13, 2010

### bon

KE before = 0.5mv^2

KE after = 1/2(m+1000)v^2..

difference = 50,000J

So please could you help with my second Q?

5. May 13, 2010

### diazona

Well, do you know about the work-energy theorem?