A body weighing 1 kg slides along an inclined plane 21 m long, which forms a zo degree with the horizon.

A body weighing 1 kg slides along an inclined plane 21 m long, which forms a zo degree with the horizon. The speed of the body at the base of the inclined plane is 4.1 m / s. Calculate the amount of heat that is released when a body friction against an inclined plane, if the initial velocity of the body is zero.

Being at the upper point of the inclined plane, the body had potential energy Wp, which was spent on the acquisition of kinetic energy Wc and the release of heat during friction Q:
Wп = Wк + Q;
Q = Wп-Wк.
Height h, at which the body was at the initial moment:
h = L * sin 30 °, where L is the length of the inclined plane:
Q = mgh – mv² / 2 = m (gL * sin 30 ° – v² / 2) = 1 kg (9.8 m / s² * 21 m * 0.5 – 4.1² / 2 m² / s²) = 95 J …
Answer: 95 J.