A force separately produces accelerations of $18 \mathrm{~ms}^{-2}$, $9 \mathrm{~ms}^{-2}$ and $6 \mathrm{~ms}^{-2}$ in three bodies of masses $P, Q$ and $R$ respectively. If the same force is applied on a body of mass $P+Q+R$, then the acceleration of that body is

If the system of blocks shown in the figure is released from rest, the ratio of the tensions $T_1$ and $T_2$ is (Neglect the mass of the string shown in the figure)

A man of mass 60 kg is standing in a lift moving up with a retardation of $2.8 \mathrm{~ms}^{-2}$. The apparent weight of the man is