Question

A bullet of mass $20g$ moving with a velocity of $100m{s}^{-1}$ strikes a wooden block of mass $80g$ at rest and gets embedded into it. Calculate the velocity of the combined system.

• A. 10 ms^-1
• B. 30 ms^-1
• C. 20 ms^-1
• D. 5 ms^-1

Answer 1

The correct option is C

20 ms^-1

Given: mass of bullet $m_1=20g=0.02kg$, mass of wooden block $m_2=80g=0.08kg$, initial velocity of bullet $u_1=100m{s}^{-1}$, the block is at rest its initial velocity $u_2=0m{s}^{-1}$
Since the block and bullet moves with a common velocity later, let the common velocity of the block and bullet system as $v$
By applying law of conservation of momentum,

Initial momentum of the system = Final momentum of the system

$(0.020\times 100)+(0.080\times 0)=v\times (0.020+0.080)$
$\Rightarrow 2=v\times 0.1$
$\Rightarrow v$= $20m/s$.