A) 15 m/sec downwards
B) 15 m/sec upwards
C) 51 m/sec downwards
D) 51 m/sec upwards
Correct Answer: A
Solution :
Velocity of 50 kg. mass after 5 sec of projection \[v=u-gt\]\[=100-9.8\times 5=51\ m/s\] At this instant momentum of body is in upward direction \[{{P}_{\text{initial}}}=50\times 51=2550\ kg-m/s\] After breaking 20 kg piece travels upwards with 150 m/s let the speed of 30 kg mass is V \[{{P}_{\text{final}}}=20\times 150+30\times V\] By the law of conservation of momentum \[{{P}_{\text{initial }}}={{P}_{\text{final}}}\] Þ \[2500=20\times 150+30\times V\Rightarrow V=-15\ m/s\] i.e. it moves in downward direction.
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