A block of mass 2 kg is placed on a rough horizontal surface. If a horizontal force of 20 N acting on the block produces an acceleration of $7 \mathrm{~ms}^{-2}$ in it, then the coefficient of kinetic friction between the block and the surface is

(Acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )

The apparent weight of a girl of mass 30 kg when she is in a lift moving vertically upwards with an acceleration of $2 \mathrm{~ms}^{-2}$ is (Acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )

Two bodies $A$ and $B$ of masses 1.5 kg and 3 kg are moving with velocities $20 \mathrm{~ms}^{-1}$ and $15 \mathrm{~ms}^{-1}$ respectively. If the same retarding force is applied on the two bodies, then the ratio of the distances travelled by the bodies $A$ and $B$ before they come to rest is

Two blocks $A$ and $B$ of masses 2 kg and 4 kg respectively are kept on a rough horizontal surface. If same force of 20 N is applied on each block, then the ratio of the accelerations of the blocks $A$ and $B$ is (Coefficient of kinetic friction between the surface and the blocks is 0.3 and acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )