A body rests on a rough horizontal plane. A force = mg is applied to the body directly towards the plane at an angle q with the vertical. The body can be moved along the plane only if the value of the angle q is

The body can be pulled when horizontal component of the force is greater than the force of friction. The vertical component of the force increases the normal reaction. 

$\Rightarrow \mathrm{mgsin}\mathrm{\theta }\ge \mathrm{\mu }(\mathrm{mg}+\mathrm{mgcos}\mathrm{\theta })$

$\Rightarrow \frac{\sin \theta }{1+\cos \theta }\ge \mu$

$\Rightarrow \frac{2\sin {\displaystyle \frac{\theta }{2}}\cos {\displaystyle \frac{\theta }{2}}}{2{\left(\cos {\displaystyle \frac{\theta }{2}}\right)}^2}\ge \mu$

$\Rightarrow \tan \frac{\theta }{2}\ge \mu =\tan \alpha$          [$\alpha$ : limiting angle of friction ]

$\Rightarrow \frac{\theta }{2}\ge \alpha$

$\Rightarrow \theta >\alpha$