If action and reaction act on a body, how is the motion of the body possible?

What is the momentum of a boy of mass $40 \mathrm{kg}$ when he walks with a uniform velocity of $2 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{s}$}\right.$.

A force of $20 \mathrm{N}$ towards east is balanced by an unknown force $f$. What will be the magnitude and direction of unknown force?

The velocity-time graph of a body moving on a horizontal surface is shown in the adjoining figure. The mass of the body is $20 \mathrm{g}$. How much force does the surface exert on the body to bring it to rest?

Calculate the change in momentum of a car of mass $1500 \mathrm{kg}$ when its speed increases from $18 \mathrm{km}/\mathrm{h} \mathrm{to} 90 \mathrm{km}/\mathrm{h}$ uniformly.

For how long should a force of $100\hspace{0.17em}\mathrm{N}$ act on a body of mass $20 \mathrm{kg}$ so that it acquires a velocity of $25 \mathrm{m}/\mathrm{s}$.

A body of mass $m$ moving with a constant velocity $v$ hits another body of the same mass moving with the same velocity $v$ but in opposite direction and sticks to it. What is the velocity of the compound body after collision?

A load of 100 N is applied at one end of a spring balance and an equal load is applied at the other end at the same time. What is the reading on the balance?

A cricket ball of mass $0.32 \mathrm{kg}$ moving with a speed of $40 \mathrm{m}/\mathrm{s}$ is brought to rest in $0.2 \sec$. What is the average force applied by the player?