English Medium Class 9 - CBSE Question Bank Solutions for Science

Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.

Cite an experiment to show that sound needs a material medium for its propagation.

List any three human activities that you think would lead to air pollution.

Why is the atmosphere essential for life?

Which force is responsible for the moon revolving round the earth ?

What is the acceleration produced in a freely falling body of mass 10 kg ? (Neglect air resistance)

When an object is dropped from a height, it accelerates and falls down. Name the force which accelerates the object.

What force is responsible for the earth revolving round the sun ?

State whether the following statement is true or false :
A falling stone also attracts the earth.

State whether the following statement is true or false :

The acceleration due to gravity acting on a freely falling body is directly proportional to the mass of the body.

Fill in the following blank with suitable word :

The acceleration due to gravity on the moon is about ………………of that on the earth.

Explain what is meant by the equation :
`g= Gxxm/r^2`
where the symbols have their usual meanings.

What do you mean by the term free fall ?

During a free fall, will heavier objects accelerate more than lighter ones ?

Give reason for the following :
The force of gravitation between two cricket balls is extremely small but that between a cricket ball and the earth is extremely large.

Explain why, if a stone held in our hand is released, it falls towards the earth.

What is the force of gravity on a body of mass 150 kg lying on the surface of the earth? (Mass of earth = 6 x 10²⁴ kg; Radius of earth = 6.4 x 10⁶ m; G = 6.7 x 10^-11 Nm²/kg²)

What do you understand by the term 'acceleration due to gravity of earth' ?

What is the usual value of the acceleration due to gravity of earth ?

The values of g at six distances A, B, C, D, E and F from the surface of the earth are found to be 3.08 m/s², 9.23 m/s², 0.57 m/s², 7.34 m/s², 0.30 m/s² and 1.49 m/s², respectively.
(a) Arrange these values of g according to the increasing distances from the surface of the earth (keeping the value of g nearest to the surface of the earth first)
(b) If the value of distance F be 10000 km from the surface of the earth, state whether this distance is deep . inside the earth or high up in the sky. Give reason for your answer.