$A$ stone of $1\, kg$ is thrown with a velocity of $20\, m\ s^{-1}$ across the frozen surface of a lake and comes to rest after travelling a distance of $50\, m$. What is the force of friction (in $N$) between the stone and the ice?

An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes,state the conditions that must be placed on the magnitude and direction of the velocity. If no,provide a reason.

Why is it advised to tie any luggage kept on the roof of a bus with a rope?

Two objects,each of mass $1.5\, kg$,are moving in the same straight line but in opposite directions. The velocity of each object is $2.5\, m/s$ before the collision during which they stick together. What will be the velocity (in $m/s$) of the combined object after collision?

Two persons manage to push a motorcar of mass $1200 \, kg$ at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of $0.2 \, m \, s^{-2}$. With what force (in $N$) does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)

How much momentum will a dumbbell of mass $10\, kg$ transfer to the floor if it falls from a height of $80\, cm$? Take its downward acceleration to be $10\, m \,s^{-2}$.