An unruly demonstrator lifts a stone of mass 200g from the ground… - Vidyadip

Question

An unruly demonstrator lifts a stone of mass 200g from the ground and throws it at his opponent. At the time of projection, the stone is 150cm above the ground and has a speed of 3.00m/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?

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Answer

m = 200g = 0.2kg, h = 150cm = 1.5m, v = 3m/sec, t = 1sec Total work done $=\frac{1}{2}\text{mv}^2+\text{mgh}$ $=\Big(\frac{1}{2}\Big)\times(0.2)\times9+(0.2)\times(9.8)\times(1.5)=3.84\text{J}$ h.p. used $=\frac{3.84}{746}=5.14\times10^{-3}$

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