Question

A bullet of mass $0.01kg$ moving at a speed of $500m/sec$, strikes a block of mass $2kg$, suspended by a rope of length $5m$. If the block rises to a height of $0.1m$, then with what velocity does the bullet emerge from the block?

• A. $220m/sec$
• B. $340m/sec$
• C. $120m/sec$
• D. $250m/sec$

Answer 1

Answer: (A)

$220m/sec$

If block raises to height of $0.1m$ K.E of block after the bullet passes through it
at lowest point $=mgh$

$\frac{1}{2}m{v}^2=mgh$

$\Rightarrow v=\sqrt{2gh}$

$=\sqrt{2\times 9.8\times 0.1}$

$=\sqrt{1.96}=1.4m/s$

Using momentum conservation,

$0.01\times 500=1.4\times 2+0.01\times v$

$5-2.8=0.01\times v$

$\Rightarrow v=220m/s$