The Fundamental Unit of Life

Convert into mole.

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

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

Why is the atmosphere essential for life?

List any three reasons why you would think that you are sick and ought to see a doctor. If only one of these symptoms were present, would you still go to the doctor? Why or why not?

Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide

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

Distinguish between speed and velocity.

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

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 following giving examples.

(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension

Why is it not possible to see an atom with naked eyes?

Define the atomic mass unit.

Write a note on how forests influence the quality of our air, soil and water resources.

What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

Certain force acting on a 20 kg mass changes its velocity from 5 m s^-1 to 2 m s^-1. Calculate the work done by the force.

Under which of the following conditions are you most likely to fall sick?
(a) when you are taking examinations.
(b) when you have travelled by bus and train for two days.
(c) when your friend is suffering from measles.

Why?

A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.

Name the regions in which parenchyma tissue is present.

Name the technique to separate

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

A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:

(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.