How to Calculate Power in a Physics Problem?

[dorkymichelle]

Homework Statement

A 50-N force acts on a 2-kg crate that starts from rest. When the force has been acting for 2 s the rate at which it is doing work is:

Homework Equations

I used F = ma, d= Vit+1/2at^2, w=F*d, Power = W/t,

The Attempt at a Solution

F=ma, 50=2*a, a=25
d= 0*2+1/2(25)(2)^2
d=50
W = 50*50 = 2500
P = 2500/2 = 1250 and that's not on the multiple choice list.. I'm guessing I found the wrong distance?

 

[the_kool_guy]

this u have calculated is average power in 2 sec .instantaneous is F.v
i think its 2500...

do tell me if i am correct

 

[dorkymichelle]

You're right!
You got V from kinematics right?
I did Vf = vi+at
so Vf = 0+(25)*2
and then 50*50=2500 ?

 

[the_kool_guy]

yeah