The rate of change of momentum is

Two similar vehicles are moving with the same velocity on roads,such that one of them is loaded and the other is empty. Which of the two vehicles will require a larger force to stop it? Give reasons.

$A$ man weighing $60 \ kg$ runs along the rails with a velocity of $18 \ km \ h^{-1}$ and jumps into a car of mass $1$ quintal $(100 \ kg)$ standing on the rails. Calculate the velocity with which the car will start travelling along the rails. (in $m \ s^{-1}$)

What force would be needed to produce an acceleration of $4 \, m s^{-2}$ on a ball of mass $6 \, kg$?

$(a)$ 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 $10 \, kg$.

$A$ certain force exerted for $1.2 \, s$ raises the speed of an object from $1.8 \, m s^{-1}$ to $4.2 \, m s^{-1}$. Later, the same force is applied for $2 \, s$. How much does the speed change in $2 \, s$?