Two bodies having same mass $40\, kg$ are moving in opposite directions,one with a velocity of $10\, m/s$ and the other with $7\, m/s$. If they collide and move as one body,the velocity of the combination is ........ $m/s$.

$A$ smooth sphere is moving on a horizontal surface with a velocity vector $(2 \hat{i} + 2 \hat{j}) \ m/s$ immediately before it hits a vertical wall. The wall is parallel to the vector $\hat{j}$ and the coefficient of restitution between the sphere and the wall is $e = 1/2$. The velocity of the sphere after it hits the wall is:

In an inelastic collision,after collision the kinetic energy

$A$ ball is moving with speed $20 \, m/s$ collides with a smooth surface as shown in the figure. The magnitude of the change in velocity of the ball will be ........... $m/s$.

In an inelastic collision,what is conserved?

$A$ body falls from a height of $10 \ m$ onto the ground and rebounds to a height of $2.5 \ m$. The percentage loss in kinetic energy is ......... $\%$.