$A$ truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of $400 \, m$ in $20 \, s$. Find the force (in $N$) acting on it if its mass is $7 \, \text{tonnes}$ $(1 \, \text{tonne} = 1000 \, kg)$.

Explain,why is it difficult for a fireman to hold a hose,which ejects large amounts of water at a high velocity.

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?

An object of mass $100 \,kg$ is accelerated uniformly from a velocity of $5 \,m \,s^{-1}$ to $8 \,m \,s^{-1}$ in $6 \,s$. Calculate the initial and final momentum of the object. Also, find the magnitude of the force exerted on the object.

$A$ hockey ball of mass $200 \,g$ travelling at $10 \,m \,s^{-1}$ is struck by a hockey stick so as to return it along its original path with a velocity of $5 \,m \,s^{-1}$. Calculate the magnitude of the change in momentum of the hockey ball due to the force applied by the hockey stick.

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.)