If n balls hit elastically and normally on a surface per unit time and all balls of mass m are movin

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4-1.Newton's Laws of Motion

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If $n$ balls hit elastically and normally on a surface per unit time and all balls of mass $m$ are moving with same velocity $u$, then force on surface is ..........

A

$mun$

B

$2 \,mun$

C

$\frac{1}{2} m u^2 n$

D

$m u^2 n$

Solution

(b)

As collision is elastic, velocity after the collision will be $-u$

So using $F=\frac{d p}{d t}$

$=n(m u-(-m u)$

$=2 \,n m u$

Standard 11

Physics

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