A) 2 m/s
B) 4 m/s
C) 8 m/s
D) 0.2 m/s
Correct Answer: A
Solution :
Key Idea: Linear momentum of a system is conserved in absence of any external force. Conservation of linear momentum gives \[{{m}_{1}}\,{{u}_{1}}+{{m}_{2}}\,{{u}_{2}}=({{m}_{1}}+{{m}_{2}})v\] Given, \[{{m}_{1}}=25g,\,{{u}_{1}}=400\,m/s\] \[{{m}_{2}}=4.9\,kg,\,\,{{u}_{2}}=0,\,v=?\] Hence, \[\frac{25}{1000}\times 400+4.9\times 0=\left( \frac{25}{1000}+4.9 \right)v\] or \[v=\frac{10000}{4925}\approx 2\,m/s\] Note: Since, bullet is embedded into bag, hence the collision is inelastic. But still the momentum is conserved.
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