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A disc of mass 100 g is kept floating horizontally in air by firing bullets

A disc of mass 100 g is kept floating horizontally in air by firing bullets, each of mass 5g with the same velocity at the same rate of 10 bullets/s.The bullets rebound with the same speed in opposite direction,the velocity of each bullet at the time of impact is

Options

(a) 196 cms⁻¹
(b) 9.8 cms⁻¹
(c) 98 cms⁻¹
(d) 980 cm⁻¹

Correct Answer:

980 cm⁻¹

Explanation:

Rate of change in momentum of the bullets balances weight of the plate

2m’vn = mg
.·. v = mg/2m’n = (100 x 980)/(2 x 5 x 10)
= 980 cm⁻¹

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