If $\alpha, \beta$ and $\gamma$ are the angles made by a vector with $x, y$ and $z$ axes respectively, then $\sin ^2 \alpha+\sin ^2 \beta=$

A particle moving along a straight line covers the first half of the distance with a speed of $3 \mathrm{~ms}^{-1}$, the other half of the distance is covered in two equal time intervals with speeds of $4.5 \mathrm{~ms}^{-1}$ and $7.5 \mathrm{~ms}^{-1}$ respectively, then the average speed of particle during the motion is

Water flowing through a pipe of area of cross-section $2 \times 10^{-3} \mathrm{~m}^2$ hits a vertical wall horizontally with a velocity of $12 \mathrm{~ms}^{-1}$. If the water does not rebound after hitting the wall, then the force acting on the wall due to water 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 $=10 \mathrm{~ms}^{-2}$ )