Question

A tangential force is applied on a circular object which is placed on rough horizontal surface and it starts rolling on it. Then choose the correct option(s)

• A. the frictional force may act in forward direction or is a null vector
• B. the frictional force may act in backward or is a null vector
• C. the acceleration of its centre of mass is greater than or equal to F/M.
• D. the acceleration of its centre of mass is less than or equal to F/M.

Answer 1

Answer: (A), (C)

The correct options are
A the frictional force may act in forward direction or is a null vector
C the acceleration of its centre of mass is greater than or equal to F/M.

In the absence of friction. $a_{cm}=\frac{F}{M}$

and $\alpha =\frac{F.R}{I}=\frac{FR}{\gamma M{R}^2}=\frac{F}{\gamma RM}$

or $\alpha R=\frac{1}{\gamma }\frac{F}{M}$ As $\frac{1}{\gamma }\ge 1\therefore \alpha R\ge a_{cm}$.

So, friction acts is forward direction or is null vector.