Answer
$P = 5.0~W$
Work Step by Step
We can find the acceleration:
$F = ma$
$a = \frac{F}{m}$
$a = \frac{5.0~N}{15~kg}$
$a = 0.333~m/s^2$
We can find the velocity at the end of the third second:
$v = 0+(0.333~m/s^2)(3.0~s)$
$v = 1.0~m/s$
We can find the power:
$P = F~v$
$P = (5.0~N)(1.0~m/s)$
$P = 5.0~W$
