Q. 253.6( 5 Votes )

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?

Answer :

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


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