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5.work,energy,power and collision — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics5.work,energy,power and collision1 Mark
MCQ
$Assertion$ : $n$ small balls each of mass $m$ colliding elastically each second on surface with velocity $u$. The force experienced by the surface is $2\,mnu$.

$Reason$ : On elastic collision, the ball rebounds with the same velocity.

  • ✓
    If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
  • B
    If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
  • C
    If the Assertion is correct but Reason is incorrect.
  • D
    If both the Assertion and Reason are incorrect.
✓

Answer

Correct option: A.
If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
a
In elastic collision, kinetic energy remains conserved therefore the ball rebounds with the same velocity. According to Newton’s second law
$F \times t = $ change in linear momentum.
$\therefore F \times 1 = m \times n\left( {u + u} \right) \Rightarrow F = 2\,mmu$

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