A force of 4.7 N acts on a 17 kg body initially at rest. Compute the work done by the force in (a) the first, (b) the second, and (c) the third seconds and (d) the instantaneous power due to the force at the end of the third second.
d= vit + 1/2 at^2
vf= vi + at
The Attempt at a Solution
i got parts a and d.. but b and c seem to be the problem
first, i used f= ma to get the acceleration
then i plugged it in to d= 1/2at^2 to find d, and i got it
then i did work = fd and found the work
that was part a, and it was correct
for parts b and c.. i tried to use vf = vi + at
i think the problem is that i was assuming that vi is 0, but i don't know how else to do it
and for d, i just took the velocity that i found in part c, (even though the answer i got for c was wrong) and did p = fxv to get the power and it was also correct
please help, this homework is due tonight and i'm pretty confused!