Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

Abdul, while driving to school, computes the average speed for his trip to be 20 km h^-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h^-1. What is the average speed for Abdul’s trip?

Why is the atmosphere essential for life?

Why is the weight of an object on the moon 1/6th its weight on the earth?

Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

The speed-time graph for a car is shown is Fig. 8.12.

          Fig. 8.12

(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?

What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?

Why are we normally advised to take bland and nourishing food when we are sick?

You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?

Explain the working and application of a sonar.

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

How does the force of gravitation between two objects change when the distance between them is reduced to half ?

What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?

What is the greenhouse effect?

Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?

What would happen to the life of a cell if there was no Golgi apparatus?

Compare the use of manure and fertilizers in maintaining soil fertility.

Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?

Which organisms are called primitive and how are they different from the so-called advanced organisms?

Explain how sound is produced by your school bell.