An unruly demonstrator lifts a stone of mass 200 g from the ground and throws it at his opponent. At the time of projection, the stone is 150 cm above the ground and has a speed of 3.00 m/s. Calculate the work done by the demonstrator during the process. If it takes one second for the demonstrator to lift the stone and throw, what horsepower does he use?
Mass of stone = 200 g = 0.2 kg
Speed at which the stone is thrown = 3 m/s
Height of the stone above ground at the time of projection = 150 cm = 1.5 m
Work done by the demonstrator = Total energy of the process
= Kinetic energy + Potential energy
= 1/2 × Mass × (speed)2 + Mass × acceleration due to gravity × height
= 0.5 ×0.2 × 32 + 0.2 × 9.8 × 1.5
= 0.9 + 2.94
= 3.84 J
Power = Work done/ time
= 3.84/1
= 3.84 J/sec or W
= 3.84/746 hp
= 5.14 × 10-3 hp