# Simple POWer question

1. Nov 18, 2007

### ~christina~

[SOLVED] simple POWer question

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

The electric motor of a model train accelerates the train from rest to 0.620m/s in 21.0ms. Total mass of train 875g.

Find the average power delivered to the train during the acceleration.

2. Relevant equations

$$P_{av}= W_{net}/ \Delta t$$

3. The attempt at a solution

Well..I'm not sure if this is correct...

$$W_{net} = K_f- K_i= \Delta K$$ ===> I think this is correct but not sure..

using that..

$$1/2 mv_f^2 - 1/2 mv_i^2 = 0$$

vi= 0

$$1/2 mv_f^2= 0$$

$$1/2(.875kg)(0.620m/s)^2 = .1682J$$

P= 0.1682J/ 0.021s= 8.01W====> this seems pretty small but then again it's a model train..is this correct or did I miss something?

I need to know if the way I did the question was correct since they mention acceleration but I'm not sure how would I apply that if I need to at all.

Thank you

2. Nov 18, 2007

### Dick

That's right. You used energy conservation, so you don't need to compute the acceleration etc.

3. Nov 18, 2007

### ~christina~

Oh..okay then Thanks Dick