Answer
The average power is $~~860~W$
Work Step by Step
In part (a), we found that the change in mechanical energy is $~~8600~J$
We can find the time it takes the block to increase its speed to $30~m/s$:
$v_f = v_0+at$
$t = \frac{v_f - v_0}{a}$
$t = \frac{30~m/s - 10~m/s}{2.0~m/s^2}$
$t = 10~s$
We can find the average power:
$P = \frac{8600~J}{10~s} = 860~W$
The average power is $~~860~W$
