Question

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

• 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

Answer 1

Answer: (A)

2m/sec in original direction

Answer 2

$v _ { 1 } = \left( \frac { m _ { 1 } - m _ { 2 } } { m _ { 1 } + m _ { 2 } } \right) u _ { 1 } + \frac { 2 m _ { 2 } u _ { 2 } } { m _ { 1 } + m _ { 2 } }$

Substituting m₁ = 0, $v _ { 1 } = - u _ { 1 } + 2 u _ { 2 }$

⇒ $v _ { 1 } = - 6 + 2 ( 4 )$ $= 2 \mathrm {~m} / \mathrm { s }$

i.e. the lighter particle will move in original direction with the speed of 2 m/s.