NCERT Solutions for Chapter: Force and Laws of Motion, Exercise 3: 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.  

Using a horizontal force of $200 \mathrm{N}$, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?

According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.

A bullet of mass $10 \mathrm{g}$ travelling horizontally with a velocity of $150 \mathrm{m} {\mathrm{s}}^{–1}$ strikes a stationary wooden block and comes to rest in $0.03 \mathrm{s}$. Calculate the distance of penetration of the bullet into the block. Also, calculate the magnitude of the force exerted by the wooden block on the bullet.

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.