First slide

Kinetic friction

Question

A body having kinetic energy K moving on a rough horizontal surface is stopped in a distance x. The force of friction exerted on the body is

Easy

A

$\sqrt{K} / x$
B

K/x
C

$K / \sqrt{x}$
D

Kx

Solution

Let f be the force of friction and m, the mass of the body.
$∴ Retardation a = f / m$
Let v be the initial velocity of the body, then
$v^{2} = 2 ax or \frac{1}{2} {mv}^{2} = \max$
or K = fx $(∵ ma = f)$
$∴ f = K / x$ .

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