A) 600 J
B) 800 J
C) 1000 J
D) 1200 J
Correct Answer: B
Solution :
Given,\[{{m}_{1}}=20kg,\,\,{{\mu }_{1}}=10\,\,m/s\] \[{{m}_{2}}=5kg,\,\,{{\mu }_{2}}=0\] Using law of conservation of momentum, \[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}=({{m}_{1}}+{{m}_{2}})v\] \[20\times 10+5\times 0=(20+5)\times v\] \[\therefore \] \[v=\frac{200}{25}=8\,\,m/s\] Kinetic energy of the composite mass \[=\frac{1}{2}({{m}_{1}}+{{m}_{2}}){{v}^{2}}\] \[=\frac{1}{2}(20+5)\times {{(8)}^{2}}=2.5\times 32=800\,\,J\]
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