Chapter-10

GRAVITATION 


1.     How does the force of gravitation between two objects                    change when the distance between them is reduced to half ?



2.     Gravitational force acts on all objects in proportion to their         masses. Why then, a heavy object does not fall faster than a         light object?



3.     What is the magnitude of the gravitational force between            the earth and a 1 kg object on its surface? (Mass of the                earth is 6 x 1024 kg and radius of the earth is 6.4 x 106 m.)



4.     The earth and the moon are attracted to each other by                gravitational force. Does the earth attract the moon with a            force that is greater or smaller or the same as the force with         which the moon attracts the earth? Why?



5.     If the moon attracts the earth, why does the earth not move         towards the moon?


6.     What happens to the force between two objects, if

    (i) the mass of one object is doubled?

    (ii) the distance between the objects is doubled and tripled?

    (iii) the masses of both objects are doubled?


7.     What is the importance of universal law of gravitation? 8.            What is the acceleration of free fall?


9.     What do we call the gravitational force between the earth             and an object?


10.     Amit buys few grams of gold at the poles as per the                      instruction of one of his friends. He hands over the same              when he meets him at the equator. Will the friend agree              with the weight of gold bought? If not, why? [Hint: The              value of g is greater at the poles than at the equator.]


11.     Why will a sheet of paper fall slower than one that is                       crumpled into a ball?


12.     Gravitational force on the surface of the moon is                          only as strong as gravitational force on the earth. What is              the weight in newtons of a 10 kg object on the moon and on           the earth?


13.     A ball is thrown vertically upwards with a velocity of 49             m/s. Calculate

    (i) the maximum height to which it rises,

    (ii) the total time it takes to return to the surface of the earth.


14.     A stone is released from the top of a tower of height 19.6 m.          Calculate its final velocity just before touching the ground.


15.     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?


16.     Calculate the force of gravitation between the earth and              the Sun, given that the mass of the earth = 6 x 1024 kg and of           the Sun = 2 x 1030 kg. The average distance between the two           is 1.5 x 10¹¹ m.


17.     A stone is allowed to fall from the top of a tower 100 m                 high and at the same time another stone is projected                     vertically upwards from the ground with a velocity of 25             m/s. Calculate when and where the two stones will meet.


18.     A ball thrown up vertically returns to the thrower after 6 s.         Find

(a) the velocity with which it was thrown up, 

(b) the maximum height it reaches, and 

(c) its position after 4 s. 


19.     In what direction does the buoyant force on an object                  immersed in a liquid act?


20.    Why does a block of plastic released under water come up             to the surface of water?


21.     The volume of 50 g of a substance is 20 cm³. If the density              of water is 1 g cm3, will the substance float or sink?


22.     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?


Type- Bikash Bora