Atoms and Molecules — Science STD 9 — Question

A train is travelling at a speed of 90km/h^–1. Brakes are applied so as to produce a uniform acceleration of – 0.5ms^-2. Find how far the train will go before it is brought to rest.

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.

A car is moving on a level road. If the driver turns off the engine of the car, the car’s speed decreases gradually and ultimately it comes to a stop. A student says that two forces act on the car which bring it to a stop. What could these forces be? Which of these two forces contributes more to slow down and stop the car?

Compute the number of ions present in 5.85g of sodium chloride.

Compare an electron and a proton in respect of mass and charge.

What is the difference between infrasonic waves and ultrasonic waves?

Sucrose (sugar) crystals obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or a mixture? Give reasons for the same.

Define mole. What are the two things that a mole represents?