Doubt in jee09 solution

I GOT ANSWER AS 3

PLS POINT OUT THE MISTAKE IN MY SOLUTION:

mA(9)=mBvB (Since collision is elastic)

Thus, vB=9/2 ms-1

Collision between B and C is inelastic

so 2mvB=3mvcommon

So vcommon=3 ms-1

But ans given is 4 ms-1

2 Answers

106
Asish Mahapatra ·

1 st collision:
9m = mv1 + 2mv2
u have assumed mv1=0 that is wrong
v2-v1=9

2nd collision:
find v2 from above
so, 2mv2 = 3mv
==> v = 2v2/3

1
rahul wadhwani ·

this mistake i also do but there is slight mistake in the first line that u have stopped body -a after collision which is possible when both have same mass

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