"A bullet of mass 0 01 kg and travelling at a speed of 500m/s strikes a block which is suspended - Physics - Laws of Motion

Question

"A bullet of mass 0 01 kg and travelling at a speed of 500m/s
strikes a block which is suspended by a string of length 5m The
centre of gravity of the block is found to rise a distance of 0 1m
What is the speed of bullet after it emerges from the block?"

Jyoti Pant · Accepted Answer

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Suppose v1 and v2 are the velocities of the bullet and the block after collision
Since the block rises to a height h=0
01 m, so all its kinetic energy is converted into its potential energy
Thus, by conservation of energy,12m2v22=m2ghor v2=2gh=2×9
8×0 01=1
4 m/sIf u1 is the initial velocity of the bullet, then applying the law of conservation of momentum along the initial direction of the bullet,we getm1u1=m1v1+m2v2v1=m1u1-m2v2m1=0
01×500-2×1 40 01=220 m/s

"A bullet of mass 0.01 kg and travelling at a speed of 500m/s strikes a block which is suspended by a string of length 5m. The centre of gravity of the block is found to rise a distance of 0.1m. What is the speed of bullet after it emerges from the block?"