English Medium कक्षा ९ - CBSE Question Bank Solutions for Science

A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (see the given figure). Let us take it that the force acts on the object through the displacement. What is the work done in this case?

When do we say that work is done?

Write an expression for the work done when a force is acting on an object in the direction of its displacement.

Define 1 J of work.

A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?

Look at the activity below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.

A sailboat is moving due to wind energy.

An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?

Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher.

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, as shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

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?

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

Explain how sound is produced by your school bell.

What is sound and how is it produced?

What do we get from cereals, pulses, fruits and vegetables?

How do biotic and abiotic factors affect crop production?

What are the desirable agronomic characteristics for crop improvements?

What is genetic manipulation?

State Kepler’s law which is represented by the relation r³ ∝ T².

Which of the Kepler’s laws of planetary motion led Newton to establish the inverse-square rule for gravitational force between two bodies ?

Can we apply Newton’s third law to the gravitational force ? Explain your answer.