A 1-kg block is lifted vertically 1 m at constant speed by a boy.The work done by the boy is about:

Question

Quizplus · Accepted Answer

The work done by the boy is given by the formula:
Work = Force x Distance x cos(theta)
However, since the block is lifted at constant speed, the force applied by the boy is equal and opposite to the force of gravity on the block. Therefore, the net work done on the block is zero. 
However, the work done by the boy is still equal to the work done against gravity, which is given by:
Work = mgh
where m = 1 kg, g = 9.8 m/s^2 (acceleration due to gravity), and h = 1 m
Plugging in these values, we get:
Work = (1 kg) x (9.8 m/s^2) x (1 m) = 9.8 J, which is approximately equal to 10 J (choice C).

A 1-Kg Block Is Lifted Vertically 1 M at Constant