Question

A disc of mass $1.0kg$ kept floating horizontally in air by firing bullets of mass $0.05kg$ each vertically at it, at the rate of $10$ per second. If the bullets rebound with the same speed, the speed with which these are fired will be-

• A. $0.098m/s$
• B. $0.98m/s$
• C. $9.8m/s$
• D. $98.0m/s$

Answer 1

The correct option is C $9.8m/s$

$2mnv=Mg$

$v=\frac{Mg}{2mn}$

$=\frac{10\times 980}{2\times 5\times 10}cm/s$

$=\frac{9800}{100}cm/s$

$=98cm/s$

$=9.8m/s$