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 ?

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Solution

$m = 200 g = 0.2 k g, h = 150 c m = 1.5 m$

$v = 3 m / s e c, t = 1 s e c$

Total work done $= \frac{1}{2} m v^{2} + m g h$

$= (\frac{1}{2}) \times (0.2) \times 9 + (0.2) (9.8) \times (1.5)$

$= 3.84 L$

h.p used $= \frac{3.84}{746} = (5.14) \times 10^{-} 3$

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m=200 g=0.2 kg,h=150 cm=1.5 m v=3 m/sec,t=1 sec Total work done =12mv2+mgh =(12)×(0.2)×9+(0.2)(9.8)×(1.5) =3.84 L h.p used =3.84746=(5.14)×10−3

$m = 200 g = 0.2 k g, h = 150 c m = 1.5 m$

$v = 3 m / s e c, t = 1 s e c$

Total work done $= \frac{1}{2} m v^{2} + m g h$

$= (\frac{1}{2}) \times (0.2) \times 9 + (0.2) (9.8) \times (1.5)$

$= 3.84 L$

h.p used $= \frac{3.84}{746} = (5.14) \times 10^{-} 3$