Answer
(a) $W = 206~J$
(b) $P = 68.7~watts$
Work Step by Step
(a) Since the block moves at a steady speed, the force applied by the person must be equal in magnitude to the force of kinetic friction. We can find the applied force $F$. We can assume that the coefficient of kinetic friction is 0.70.
$F = F_f$
$F = mg~\mu_k$
$F = (10~kg)(9.80~m/s^2)(0.70)$
$F = 68.6~N$
We can find the work done by the person's force. Note that the block moves a distance of 3.0 meters in 3.0 seconds.
$W = F~d$
$W = (68.6~N)(3.0~m)$
$W = 206~J$
(b) We can find the person's power output.
$P = \frac{Work}{time}$
$P = \frac{206~J}{3.0~s}$
$P = 68.7~watts$
