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Home › Grade9 › Grade 9 CBSE › Physics › Gravitation › Gravitation Worksheet-9

Gravitation Worksheet-9

Gravitation Worksheet-9

 

  1. (a) What do you mean by the term ‘free fall’ ?

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

 

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

 

  1. 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.

 

  1. Describe how the gravitational force between two objects depends on the distance between them.

 

  1. What happens to the gravitational force between two objects when the distance between them is :

(i) doubled ? (ii) halved ?

 

  1. State two applications of universal law of gravitation.

 

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

 

  1. Calculate the force of gravitation between two objects of masses 50 kg and 120 kg respectively kept at a distance of 10 m from one another. (Gravitational constant, G = 6.7 × 10–11 Nm2kg–2)

 

  1. What is the force of gravity on a body of mass 150 kg lying on the surface of the earth?

(Mass of earth = 6 × 1024 kg; Radius of earth = 6.4 × 106 m; G = 6.7 × 10–11 Nm2/kg2)

 

  1. The mass of sun is 2 × 1030 kg and the mass of earth is 6 × 1024 kg. If the average distance between the sun and the earth be 1.5 × 108 km, calculate the force of gravitation between them.

 

  1. A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be 9.8 m/s2 directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards.

 

  1. A stone falls from a building and reaches the ground 2.5 seconds later. How high is the building ? (g = 9.8 m/s2)

 

  1. A stone is dropped from a height of 20 m.

(i) How long will it take to reach the ground ?

(ii) What will be its speed when it hits the ground ?    (g = 10 m/s2)

 

  1. A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall ? (g = 9.8 m/s2)

 

  1. When a cricket ball is thrown vertically upwards, it reaches a maximum height of 5 meters.

(a) What was the initial speed of the ball ?

(b) How much time is taken by the ball to reach the highest point ?   (g =10 m/s2)

 

  1. Write the differences between mass and weight of an object.

 

  1. Can a body have mass but no weight ? Give reasons for your answer.

 

  1. A force of 20 N acts upon a body whose weight is 9.8 N. What is the mass of the body and how much is its acceleration ? (g = 9.8 m s–2).

 

  1. A stone resting on the ground has a gravitational force of 20 N acting on it. What is the weight of the stone ? What is its mass ? (g = 10 m/s2).

 

  1. An object has mass of 20 kg on earth. What will be its (i) mass, and (ii) Weight, on the moon ?

(g on moon = 1.6 m/s2).

 

Answer:

  1. The falling a body (or object) from a height towards the earth under the gravitational force of earth (with no other force acting on it) is called free fall and such a body is called ‘freely falling body’

(b) No

 

  1. Yes. When earth exerts a force of attraction on an object then the object also exerts an equal force on the earth in the opposite direction.

 

  1. Gravitational force, . The force depends upon the masses of the bodies. In case of two balls the product of masses will be less so less force will be there but in case of earth product of masses will be huge so greater force will be there.

 

  1. The force between two bodies is inversely proportional to the square of the distance between them.

That is,

 

  1. The force between two bodies is inversely proportional to the square of the distance between them.

That is,

Using the above relation;

(i) Becomes one-fourth

(ii) Becomes four times

 

  1. –

 

  1. –

 

  1. Put the values of masses and distance in the formula

Gravitational force,

4.02 × 19–9 N

 

  1. 1472 N

 

Gravitational force,

3.57 × 1022 N

 

  1. 29.4 m/s

 

  1. 30.6 m

 

  1. (i) 2s, (ii) 20 m/s

 

  1. 20.4 m

 

  1. (a) 10 m/s, (b) 1 s

 

  1. Weight = mass × acceleration due to gravity

 

  1. Yes

 

  1. 1 kg ; 20 m/s2

 

  1. 20 N; 2 kg

 

  1. (i) 20 kg     (ii) 32 N