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

Question

A disc of mass 100 g is kept floating horizontally in air by firing bullets, each of mass 5 g with the same velocity at the same rate of 10 bullets per second. The bullets rebound with the same speed in opposite direction, the velocity of each bullet at the time of impact is (A) 196 cms-1 (B) 9.8 cms-1 (C) 98 cms-1 (D) 980 cms-1

Tardigrade Admin · Accepted Answer

From law of conservation of momentum. Total momentum of bullets= Momentum of disc ie, 2m' vn = mg ∴ v = (mg/2m'n) = (100 × 980/2 × 5 × 10) = 980 cm s-1

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

196 $c m s^{- 1}$

9.8 $c m s^{- 1}$

98 $c m s^{- 1}$

980 $c m s^{- 1}$

From law of conservation of momentum.
Total momentum of bullets= Momentum of disc
ie, 2m' vn = mg
$∴ v = \frac{m g}{2 m ^{'} n} = \frac{100 \times 980}{2 \times 5 \times 10}$
$= 980 c m s^{- 1}$

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

196 cms−1

9.8 cms−1

98 cms−1

980 cms−1

From law of conservation of momentum. Total momentum of bullets= Momentum of disc ie, 2m' vn = mg ∴v=2m′nmg​=2×5×10100×980​ =980cms−1

196 $c m s^{- 1}$

9.8 $c m s^{- 1}$

98 $c m s^{- 1}$

980 $c m s^{- 1}$

From law of conservation of momentum.
Total momentum of bullets= Momentum of disc
ie, 2m' vn = mg
$∴ v = \frac{m g}{2 m ^{'} n} = \frac{100 \times 980}{2 \times 5 \times 10}$
$= 980 c m s^{- 1}$