A solid sphere of mass `10 kg` is placed on a rough surface having coefficient of friction `mu = 0.1`. A constant force `F = 7 N` is applied along a line passing through the centre of the sphere as shown in the figure. The value of frictional force on the sphere is.
.

Options

A. 1 N
B. 2 N
C. 3 N
D. 7 N

Answer

B

Explanation

(b) Let `f` be frictional force towards left for pure rolling.
`a =R prop`
where, `a = (F - f)/(m) = (7 - f)/(10)`
`prop = (tau)/(I) =(f R)/(I) = (fR)/(2/5 mR^2) = (5 f)/(2 mR)`
Hence, `(7 - f)/(10) = (5 f)/(20) rArr f = 2 N`.