Calculating Work and Power: Force of 5N on a 15kg Body at Rest

[spyroarcher]

Homework Statement

A force of 5N acts on a 15kg body initially at rest. Compute the work done by the force in: first, second, and third seconds, the instantaneous power to the force at the end of the third sec.

Homework Equations

W=fd
P=(dW)/(dt)

The Attempt at a Solution

I'm not quite sure how to work this out with just the equation W=fd, but I know work is also mass X integral of acceleration vs. position. I guess my biggest problem is not knowing where to put time...
Thanks in advance

 

[Filip Larsen]

If you had an expression for the distance, s, traveled as a function of time, then you could find the work by calculate how far the body moves from t=0 to t=1, and then again from t=1 to t=2, and once more from t=2 to t=3, and the use W = Fs (using 's' instead of 'd' in order not to confuse distance with differentiation).

For the power you should notice that P = dW/dt = d(Fs)/dt = F ds/dt = F v, under the assumption that F is constant. So you can also find power if you know the speed of the body at the time in question.