Question

A $15\text{g}$ bullet is fired horizontally at a speed of $350\text{m/s}$ into $1.2\text{kg}$ block that hangs by a vertical string as shown below. The bullet remains embedded in the block. Find the speed of the bullet and the block.

• A. $10\text{m/s}$
• B. $22.5\text{m/s}$
• C. $350\text{m/s}$
• D. $4.32\text{m/s}$

Answer 1

The correct option is D $4.32\text{m/s}$



Let $V_1=$ speed of bullet $=350\text{m/s}$
$V_2=$ initial speed of block $=0$
$V=$ final speed of block & bullet
(final speed will be same for the block & bullet because bullet is embedded in the block)
By conservation of momentum,
$P_i=P_f$
$m_1{v}_1+m_2{v}_2=(m_1+m_2)V$
$\Rightarrow \left(0.015\right)\times 350+1.2\times 0=(0.015+1.2)\times V$
$\Rightarrow V=4.32\text{m/s}$