In the figure shown, find the velocity of the 3kg mass after 10s if the system is released from rest at t=0. (Take g=10m/s2)
A
30m/s
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B
40m/s
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C
50m/s
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D
70m/s
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Solution
The correct option is B40m/s The FBD of the blocks are shown in the below figure
So, from the FBD we have 7g−T=7a......(i) T−3g=3a.......(ii) From the eq (i) & (ii), we get a=4g10=4m/s2 From equation of motion we have, v=u+at ⇒v=0+4×10=40m/s
OR
a=(Supporting force - opposing Force) Total mass =7g−3g10=4m/s2 From equation of motion we have, v=u+at ⇒v=0+4×10=40m/s