Four blocks of same mass connected by strings are pulled by a force $$F$$ on a smooth horizontal surface as shown in figure. The tension $$T_1, T_2$$ and $$T_3$$ will be

A body of mass $$5 \times 10^{-3} \mathrm{~kg}$$ is launched upon a rough inclined plane making an angle of $$30^{\circ}$$ with the horizontal. Obtain the coefficient of friction between the body and the plane if the time of ascent is half of the time of descent.