A box is placed on an inclined plane and has to be pushed down. The angle of inclination is

1. equal to the angle of friction
2. more than the angle of friction
3. equal to the angle of repose
4. less than the angle of repose

The escape velocity from the earth is about 11. The escape velocity from a planet having twice the radius and the same mean density as the earth is

1. 22 
2. 11 
3. 5.5 
4. 15.5 

A particle having a charge 10 mC is held fixed on a horizontal surface. A block of mass 80 g and having charge stays in equilibrium on the surface at a distance of 3 cm from the first charge. The coefficient of friction between the surface and the block is . Find the range within which the charge on the block may lie

1. 
2.
3.
4. 

Two short magnets of equal dipole moments M are fastened perpendicularly at their centres as given in the figure. The magnitude of the magnetic filed at a distance d from the centre on the bisector of the right angle is 

1. $\frac{{\mu }_0}{4\pi }\frac{m}{d^3}$

2. $\frac{{\mu }_0}{4\pi }\frac{\sqrt{2}M}{d^3}$

3. $\frac{{\mu }_0}{4\pi }\frac{2\sqrt{2}M}{d^3}$

4.  $\frac{{\mu }_0}{4\pi }\frac{2M}{d^3}$