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
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
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
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