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Work Done by Force of Gravity

A man weighin...

Question

A man weighing $80$ kg climbs a staircase carrying a $20$ kg load. The staircase has $40$ steps, each of $25$ cm height. If he takes $20$ seconds to climb, the work done is?

49

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40

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98 \times 10^{5}

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7840

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Solution

The correct option is A $49$ W
$P o t e n t i a l e n e r g y = m a s s \times a c c e l e r a t i o n d u e t o g r a v i t y x - h e i g h t$
$P . E . = m \times g \times h$
According to the given condition -
$m = 80 + 20 = 100 k g$
$g = 9.8 m / s^{2}$
$h = 25 \times 40 = 1000 c m = 1 m$
$P . E = W o r k D o n e = 100 \times 9.8 \times 1 = 980 J$
Power is rate of work done = $\frac{W o r k D o n e}{T i m e T a k e n} = \frac{980}{20} = 49 J / s = 49$ Watt

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