An object of mass $2\, kg$ is sliding with a constant velocity of $4\, m\, s^{-1}$ on a frictionless horizontal table. The force required to keep the object moving with the same velocity is (in $, N$)

$(a)$ State Newton's third law of motion and give two examples to illustrate the law.
$(b)$ Calculate the force required to produce:
$(i)$ an acceleration of $2.5 \, m s^{-2}$ in a body of $4 \, kg$.
$(ii)$ an acceleration of $3 \, m s^{-2}$ in a body of $10 \, kg$.

While playing football,the goalkeeper did not get sufficient time to stop a fast ball shot towards him. Why did he hurt his hand while doing so?

What is momentum? Write its $SI$ unit. Interpret force in terms of momentum. Represent the following graphically:
$(a)$ Momentum versus velocity when mass is fixed.
$(b)$ Momentum versus mass when velocity is constant.

Which of the following statements is not correct for an object moving along a straight path in an accelerated motion?

$A$ jet engine works on the principle of Newton's: