How is our atmosphere different from the atmospheres on Venus and Mars?

Convert into mole.

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

Why is the atmosphere essential for life?

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?

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

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

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?

In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?
  •  if you get jaundice,
  •  if you get lice,
  •  if you get acne.

Why?

Name the technique to separate

(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.

What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?

A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.

What is the importance of universal law of gravitation?

If action is always equal to the reaction, explain how a horse can pull a cart.

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
  • Suma is swimming in a pond.
  •  A donkey is carrying a load on its back.
  •  A wind-mill is lifting water from a well.
  •  A green plant is carrying out photosynthesis.
  •  An engine is pulling a train.
  •  Food grains are getting dried in the sun.
  •  A sailboat is moving due to wind energy.

Explain the basis for grouping organisms into five kingdoms.

How many atoms are present in a

(i) H₂S molecule and
(ii) PO₄^3- ion?

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?

Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.

A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.

Explain how defects in a metal block can be detected using ultrasound.

Convert the following temperature to celsius scale:

a. 300 K              b. 573 K.