question_answer

A particle of mass m moving with horizontal speed 6 m/sec as shown in figure. If \[m<<M\] then for one dimensional elastic collision, the speed of lighter particle after collision will be                                    [MP PMT 2003]

A)          2m/sec  in original direction

B)          2 m/sec opposite to the original direction

C)          4 m/sec opposite to the original direction

D)          4 m/sec in original direction

Correct Answer: A

Solution :

          \[{{v}_{1}}=\left( \frac{{{m}_{1}}-{{m}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)\,{{u}_{1}}+\frac{2{{m}_{2}}{{u}_{2}}}{{{m}_{1}}+{{m}_{2}}}\]               Substituting m1 = 0, \[{{v}_{1}}=-{{u}_{1}}+2{{u}_{2}}\]               Þ \[{{v}_{1}}=-\,6+2(4)\] \[=2m/s\]               i.e. the lighter particle will move in original direction with the speed of 2 m/s.