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Question

# Two stones are dropped down simultaneously from different heights with initial speed u1=0 and u2=30 m/s respectively. If the initial distance between them is 10 m and mass of the first stone is twice that of the second stone, find the velocity of their COM after 2 s. [Take g=10 m/s2]

A
20 m/s
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B
30 m/s
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C
50 m/s
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D
10 m/s
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Solution

## The correct option is B 30 m/sGiven, u1=0,u2=30 m/s Let the mass of the second stone be m. Then, mass of the first stone will be 2m. Acceleration of COM is g m/s2 Initial velocity of COM, ucom=m1u1+m2u2m1+m2 =2m×0+m×30m+2m=10 m/s Velocity of COM after 2 s will be vcom=ucom+acom×t vcom=10+10×2=30 m/s

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