Class 9 Science - Chapter Work and Energy NCERT Solutions | A lamp consumes 1000 J of electrical ene

An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?

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?

A freely falling object eventually stops on reaching the ground. What happenes to its kinetic energy?

Define 1 J of work.

In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?

The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?

The kinetic energy of an object of mass, m moving with a velocity of 5 m s^-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?

A certain household has consumed 250 units of energy during a month. How much energy is this in joules?

Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?

State the universal law of gravitation.

Which of the following are matter?

Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.

What is meant by a pure substance?

How does the sound produced by a vibrating object in a medium reach your ear?

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.

sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

What are canal rays?

State any two conditions essential for good health.

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

Who discovered cells, and how?

What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?

Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?

Can you name the two organelles we have studied that contain their own genetic material?

Give reasons for the following observation:

The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.

How many atoms are present in a

(i) H₂S molecule and
(ii) PO₄^3- ion?

A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h^-1 in 10 minutes. Find its acceleration.

List any three human activities which would lead to an increase in the carbon dioxide content of air.

Why is it difficult to hold a school bag having a strap made of a thin and strong string?

Define valency by taking examples of silicon and oxygen.