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