# Class 9 Gravitation Important Questions

Gravitation Important Questions

1. An object is thrown vertically upward and rises to height of 10 m. Calculate the (i) the velocity by which the object was thrown upward and (ii) the time taken by object to reach the highest point.
2. The mass of earth is 6.4 x 1024 kg and that of the moon is 7.4 x 1022 kg. If the distance between the earth and the moon is 3.84 × 105 km, calculate the force exerted by the earth on the moon. (G = 6.7 × 10-11 N m2 kg-2).
3. Two bodies of masses 3 kg and 12 kg are placed at a distance 12 m. A third body of mass 0.5 kg is to be placed at such a point that the force acting on this body is zero. Find the position of that point.
4. A block of wood is kept on a tabletop. The mass of wooden block is 5 kg and its dimensions are 40 cm x 20 cm x 10 cm. Find the pressure exerted by the wooden block if it is made to lie on the table top with its sides of dimensions (a) 20 cm × 10 cm and (b) 40 cm × 20 cm.
5. Calculate the force of gravitation between the earth and the Sun, given that the mass of the earth = 6 × 1024 kg and of the Sun = 2 × 1030 kg. The average distance between the two is 1.5 × 1011 m.
6. A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking g = 10 m/s2, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?
7. What do we call the gravitational force between the earth and the object ?
8. A stone is allowed to fall from the top of tower 100 m high and at the same time another stone is projected vertically upward from the ground with the velocity of 25 m/s. Calculate when and where the two stones will meet.
9. Show that the weight of the body on moon is 1/6 of the weight of the body on earth.
10. Calculate value of ‘g’ on moon .
11. A person can lift a mass of 15 kg on the earth. What will be the maximum mass which can be lifted by the same force applied by the person on the moon?
12. A stone and feather are thrown from a tower, both the objects should reach the ground at same time but it does not. Why?
13. A ball projected vertically upward with an initial velocity of u goes to a maximum height h before coming to ground. What is the value of h?
14. What will happen to the gravitational force between two bodies if the mass of one body is doubled?
15. Prove that if the earth attracts two bodies placed at same distance from the centre of the earth with the same force, then their masses are equal.
16. Differentiate between acceleration due to gravity (g) and universal gravitation constant (G).
17. During a free-fall, what is the weight of a body. Give reason for the answer.
18. Calculate the buoyant force acting on an object immersed in water, if the object displaces 4 kg of water.
19. The volume of 50 g of a substance is 20 cm3. (The density of water is 1 g cm-3 and g = 10 ms-2)
1. Will the substance float or sink?
2. What is the volume and mass of water displaced?
3. Calculate the buoyant force acting on the substance?
20. The volume of a 500 g sealed packet is 350 cm3. Will the packet float or sink in water if the density of water is 1 g cm-3? What will be the mass of the water displaced by this packet? What will be the buoyant force acting on the packet ?