Question

Figure shows a disc which is rolling without slipping. The magnitude and direction of frictional force acting on the disc is

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Assuming the direction of frictional force opposite to the direction of external force opposite to the direction of external force, the value of frictional force can be calculated by,

f = $\frac{F(\frac{K^2}{R^2}-\frac{x}{r})}{1+\frac{K^2}{R^2}}$
where x = perpendicular distance of 'F' from centre of the rolling body.

For disc $\frac{K^2}{R^2}$ = $\frac{1}{2}$ as per the given data x = R.

$\Rightarrow$ f = $\frac{10(\frac{1}{2}-\frac{R}{R})}{1+\frac{1}{2}}$ = $\frac{-10}{2}$ N

'-' denotes that direction of frictional force is along with the external force.

$\therefore$ f = $\frac{10}{3}$ N in the direction of external force.