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Question: A disk of mass 10 g is kept floating horizontally in the air by firing bullets each of mass 5 g with...

A disk of mass 10 g is kept floating horizontally in the air by firing bullets each of mass 5 g with the same velocity. If 10 bullets are fired per second and the bullets rebound with the same velocity, then the velocity of each bullet is –

A

196 cm/sec

B

98 cm/sec

C

49 cm/sec

D

none of these

Answer

98 cm/sec

Explanation

Solution

2mnv = mg

 v = Mg2mn\frac{Mg}{2mn} = (10×10−3)×9.82(5×10−3)×10\frac{(10 \times 10^{- 3}) \times 9.8}{2(5 \times 10^{- 3}) \times 10}

= 0.98 m/s = 98 cm/s