The coefficient of friction between a body

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The coefficient of friction between a body and the surface of an inclined plane at $45^°$ is $0.5.$ If $g = 9.8\,m/{s^2}$, the acceleration of the body downwards in $m/{s^2}$ is

A

$\frac{{4.9}}{{\sqrt 2 }}$

B

$4.9\sqrt 2 $

C

$19.6\sqrt 2 $

D

$4.9$

The coefficient of friction between a body and the surface of an inclined plane at $45^°$ is $0.5.$ If $g = 9.8\,m/{s^2}$, the acceleration of the body downwards in $m/{s^2}$ is

$a = g(\sin \theta - \mu \cos \theta ) = 9.8(\sin 4{5^o} - 0.5\cos {45^o})$
$ = \frac{{4.9}}{{\sqrt 2 }}\;m/{\sec ^2}$