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Work, Energy, and Power — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsWork, Energy, and Power3 Marks
Question
What is an elastic collision? What will happen, when
  1. A heavy body collides with a light mass at rest.
  2. A light body collides with a heavy mass at rest.
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Answer

Elastic collision is one in which both momentum and energy are conserved. We know, when two bodies m1 and m2 moving with velocities u1 and u2 collide, their velocities become,

$\text{v}_1=\frac{(\text{m}_1-\text{m}_2)\text{u}_1+2\text{m}_2\text{u}_2}{\text{(m}_1+\text{m}_2}$

$\text{v}_2=\frac{\text{m}_2-\text{m}_1)\text{u}_2+2\text{m}_1\text{u}_1}{(\text{m}_1+\text{m}_2)}$

  1. if m1 >> m2 and u2 = 0, we get 

$\text{v}_1=\frac{\text{m}_1\text{u}_1}{\text{m}_1}=\text{u}_1,\text{v}_2=2\text{u}_1$

  1. If m1 >> m2 and u1 = 0, we get 

$\text{v}_1=\frac{2\text{m}_2\text{u}_2}{\text{m}_1}, $ as m2 << m1

$\therefore\text{v}_1\approx0$

$\text{v}_2=-\frac{\text{m}_1\text{u}_2}{\text{m}_1}=-\text{u}_2$

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