The driver of a three-wheeler moving with a speed of $36\; km/h$ sees a child standing in the middle of the road and brings his vehicle to rest in $4.0\; s$ just in time to save the child. What is the average retarding force (in $N$) on the vehicle? The mass of the three-wheeler is $400\; kg$ and the mass of the driver is $65\; kg$.

If the mass and the acceleration of an object are both doubled,how does the force acting on the object change with respect to its previous value?

An object of mass $2 \, kg$ is placed at rest in a frame $S_1$ moving with velocity $10 \hat{i} + 5 \hat{j} \, m/s$ and having acceleration $5 \hat{i} + 10 \hat{j} \, m/s^2$. The object is also seen by an observer standing in a frame $S_2$ moving with velocity $5 \hat{i} + 10 \hat{j} \, m/s$. Calculate the net force acting on the object with respect to the $S_1$ frame.

The average resisting force that must act on a $5 \,kg$ mass to reduce its speed from $65 \,cm/s$ to $15 \,cm/s$ in $0.2 \,s$ is .......... $N$.

$A$ body of mass $5 \ kg$ is moving in a straight line. The relation between its displacement and time is $x = (t^3 - 2t - 10) \ m$. What is the force acting on it at the end of $5 \ s$ (in $N$)?

$A$ bullet of mass $20 \,g$ moving with $500 \,ms^{-1}$ is pierced $1 \,cm$ into a wooden block. The retarding force experienced by the bullet is: