When a belt moves horizontally at a constant speed of 1.5ms−1, gravels are falling on it at rate of 5kg s−1. Then, the extra power required to drive the belt is
A
11.25W
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B
37.5W
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C
7.5W
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D
0.75W
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Solution
The correct option is A11.25W It is given that the velocity of the belt v=1.5ms−1
The rate at which the mass of the gravel falls is given by
dmdt=5kgs−1
By the newtons second law, we know that force is the rate of change of momentum (p=mv)
F=dpdt=dvdtm+dmdtv=5×1.5=7.5N (As the velocity v is constant, change in velocity dv=0)