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JEE Main 20154 April
Exam
JEE Main
Year
2015
Date
4 April
Subject
Physics
Chapter
Center of Mass, Momentum and Collision

JEE Main 2015 · 4 April · Physics · Center of Mass, Momentum and Collision

A particle of mass m moving in the x direction with speed 2v is hit...

A particle of mass m\text{m} moving in the xx direction with speed 2v2v is hit by another particle of mass 2m2m moving in the yy direction with speed v.v . If the collision is perfectly inelastic, the percentage loss in the energy during the collision is close to:A particle of mass m moving in the x direction with speed 2v is hit by another particle of mass 2m moving in the y

Options

  1. A6262 %
  2. B4444 %
  3. C5050 %
  4. D5656 %

Correct answer

D. 5656 %

Step-by-step solution

The initial momentum of system is \overset{\to}{{P}_{i}} = m\left(2V\right)\overset{^}{i} + \left(2m\right)V\overset{^}{j}

According to question as

A particle of mass m moving in the x direction with speed 2v is hit by another particle of mass 2m moving in the y

On perfectly inelastic collision the particles stick to each other.

Pf→=3mVf→\overset{\to}{{P}_{f}} = 3m\overset{\to}{{V}_{f}}

By conservation of linear momentum

\overset{\to}{{P}_{f}} = \overset{\to}{{P}_{i}} ⇒ 3m\overset{\to}{{V}_{f}} = m2V\overset{^}{i} + 2mV\overset{^}{j}

⇒ \overset{\to}{{V}_{f}} = \dfrac{2V}{3}\left(\overset{^}{i} + \overset{^}{j}\right) ⇒ | {V}_{f} | = \dfrac{2\sqrt{2}}{3}V

∴∴ loss in KE. of system =Kinitial−Kfinal= {K}_{initial} - {K}_{final}

=12m(2V)2+12(2m)V2−12(3m)(22V3)2= \dfrac{1}{2}m{\left(2V\right)}^{2} + \dfrac{1}{2}\left(2m\right){V}^{2} - \dfrac{1}{2}\left(3m\right){\left(\dfrac{2 \sqrt{2} V }{3}\right)}^{2}

=2mV2+mV2−43mV2=3mV2−4mV23=53mV2= 2m{V}^{2} + m{V}^{2} - \dfrac{4}{3}m{V}^{2} = 3m{V}^{2} - \dfrac{4m{V}^{2}}{3} = \dfrac{5}{3}m{V}^{2}

% Loss in KE =100×∆KKi=53mv23mV2=59×100=56= 100 \times \dfrac{∆ K}{{K}_{i}} = \dfrac{\dfrac{5}{3}m{v}^{2}}{3m{V}^{2}} = \dfrac{5}{9} \times 100 = 56%
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