A) 4 km/hr
B) 3 km/hr
C) 2 km/hr
D) 1 km/hr
Correct Answer: D
Solution :
Here: Mass of the body\[{{m}_{1}}=m\] Velocity of the first body \[{{u}_{1}}=312\,m/\sec \] Mass of second body at rest \[{{m}_{2}}=2\,m\] Velocity of second body \[{{u}_{2}}=0\] After combination total mass of the body \[M=m+2m=3m\]Now from the law of conservation of momentum \[M\upsilon ={{m}_{1}}\,{{u}_{1}}+{{m}_{2}}\,{{u}_{2}}\] (where \[M=m+2\,m=3m)\] \[3m\upsilon =m\times 3+2m\times 0\] \[\upsilon =1\,km/hr\]
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