A stone of $1\, kg$ is thrown with a velocity of $20\, m\ s^{-1}$ across the frozen surface of a lake and comes to rest after travelling a distance of $50\, m$. What is the force of friction(in $N$) between the stone and the ice?

Akhtar, Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change in momentum as compared to the change in momentum of the motorcar (because the change in the velocity of the insect was much more than that of the motorcar). Akhtar said that since the motorcar was moving with a larger velocity, it exerted a larger force on the insect. And as a result the insect died. Rahul while putting an entirely new explanation said that both the motorcar and the insect experienced the same force and a change in their momentum. Comment on these suggestions.

If action is always equal to the reaction, explain how a horse can pull a cart.

When a carpet is beaten with a stick, dust comes out of it. Explain.

A $8000 \,kg$ engine pulls a train of $5 $ wagons, each of $2000\, kg$, along a horizontal track. If the engine exerts a force of $40000 \,N $ and the track offers a friction force of $5000\, N$, then calculate:  the acceleration(in $m/s^2$) of the train