Exercises

Why is it advised to tie any luggage kept on the roof of a bus with a rope? 

 A $8000 \mathrm{kg}$ engine pulls a train of $5$ wagons, each of $2000 \mathrm{kg}$, along a horizontal track. If the engine exerts a force of $40000 \mathrm{N}$ and the track offers a friction force of $5000 \mathrm{N}$, then calculate the net accelerating force. 

 A $8000 \mathrm{kg}$ engine pulls a train of $5$ wagons, each of $2000 \mathrm{kg}$, along a horizontal track. If the engine exerts a force of $40000 \mathrm{N}$ and the track offers a friction force of $5000 \mathrm{N}$, then calculate the acceleration of the train.  

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

An object of mass $1 \mathrm{k}\mathrm{g}$ travelling in a straight line with a velocity of $10 \mathrm{m} {\mathrm{s}}^{–1}$ collides with, and sticks to, a stationary wooden block of mass $5 \mathrm{k}\mathrm{g}$. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.

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

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.

How much momentum will a dumb-bell of mass $10 \mathrm{k}\mathrm{g}$ transfer to the floor if it falls from a height of $80 \mathrm{c}\mathrm{m}$? Take its downward acceleration to be $10 \mathrm{m} {\mathrm{s}}^{–2}$.