Question

A boy slides on his skateboard on a special curved track. It starts from the top 3.9 m of the track and reaches the lowest level with a speed of 6.2 m / s. What work did the frictional force do on him? The boy and his skateboard weigh 43 kg

Answer 1

The initial mechanical energy plus the work of the frictional force is equal to the final mechanical energy.

Ei + Tr = Ef

The initial energy is potential energy and the final energy is kinetic.

Rt = Ef-Ei = 1/2. 43 kg (6.2 m / s) ² - 43 kg. 9.80 m / s². 3.9 m = -817 J

The friction work is always negative.