Assertion : n small balls each of mass m colliding elastically ea… - Vidyadip

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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