A block of mass 1.5 kg moves along the floor of a hall with a speed of $5 \mathrm{~ms}^{-1}$. It strikes an uncompressed spring and compresses it till the block becomes motionless. If the force constant of the spring is $10000 \mathrm{Nm}^{-1}$ and the spring is compressed by 5 cm , calculate the effective force of kinetic friction.

A ball falls under gravity from a height of 10 m with an initial downward velocity u . It loses one third of its energy in collision and then rises back to 5 m . The initial velocity u is $\left(\mathrm{g}=10 \mathrm{~ms}^{-2}\right)$

A scooter moves with a speed of $$7 \mathrm{~ms}^{-1}$$, on a straight road and is stopped by applying the brakes. Before stopping, the scooter travels $$10 \mathrm{~m}$$. If the weight of the scooter is $$\mathrm{W}$$, then the total resistance to the motion of the scooter will be