Why are the ceilings of concert halls curved?

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.

In the following example, try to identify the number of times the velocity of the ball changes: “A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team”.
Also identify the agent supplying the force in each case.

Distinguish between loudness and intensity of sound.

Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

How do substances like CO2 and water move in and out of the cell? Discuss.

The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?

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

How does an Amoeba obtain its food?

Name A,B,C,D,E and F in the following diagram showing change in its state

An electric heater is rated 1500 W. How much energy does it use in 10 hours?

Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.