A) \[15\,cm{{s}^{-1}}\]towards west
B) \[15\,cm{{s}^{-1}}\]towards east
C) \[5\,cm{{s}^{-1}}\]towards west
D) \[5\,cm{{s}^{-1}}\]towards east
Correct Answer: C
Solution :
Let velocity towards east be positive, then velocity towards west is negative. If \[v\] is the velocity of two lumps which are coalesced after collision, then from law of conservation of linear momentum \[{{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}}=({{m}_{1}}+{{m}_{2}})v\] \[10\times 20-10\times 10=20\times v\] \[\Rightarrow \] \[v=\frac{100}{200}=5cm{{s}^{-1}}\] Hence, \[5cm{{s}^{-1}}\] towards west.
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