Answer:
Step-by-step explanation:
By work - energy theorem on the box
Wmg + wn + wf = kf - ki
=> mgh + 0 + wf = 1/2 mv^2f - 1/2mv^2i
=> wf = 1/2mv^2f - 1/2mv^2i - mgh
:. Wf = 1/2×2.5×4^2 - 0- 2.5×9.8×1.5
= 20 - 36.75
= -16.75 J
Work done comes out negative here which is expected as the friction always act opposite to the velocity of an object. Friction is a non conservative force and it causes loss of mechanical energy.