Question 401263
a) Use the equation {{{F[f] = mu*N}}}, where {{{mu}}} is the coefficient of kinetic friction, and N is the normal force. Substituting, we get


{{{F[f] = (0.25)(94kg)(9.8m/s^2) = 230.3}}} (Newtons)


The net force is zero (net force meaning sum of all the forces), since the crate is pushed at a constant velocity (hence no acceleration), so a 230.3 N force is required.


b) Work = force*distance. The work done by the person is given by {{{(230.3N)*(5.2m) = 1198}}} (joules). However, the net work done on the block is still zero because the net force on the block is zero.


c) Power is the rate that work is done, so Power = Work/time. We know the work done by the person is 1198 J. We need to find the amount of time taken.


We know that distance = rate*time, so 5.2 m = (0.40 m/s)*time. Solving, we get time = 13 seconds.


Therefore, Power = (1198 J)/(13 s) = 92.1 Watts.