Page 2 - IX-PHY-CH- 9-GRAVITATION
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Reason: Gravitational force exerted on heavier bodies is always equal to lighter bodies
                 because gravitational acceleration on Earth does not depend on the mass of object.

                 Subjective Questions:
                    1.   Two objects of masses m1 and m2 having the same size drop simultaneously from the
                        heights, h1 and h2 respectively. Find out the ratio of time they would take in reaching the
                        ground. Will this ratio remains the same If :
                        a)  One of the objects is hollow and the other one is solid
                        b)   both of them are hollow, size remaining the same in each case? Give a reason. (3M)
                    2.   A man is standing at the top of a 60 m high tower. He throws a ball vertically
                        upwards with a velocity of 20 m/s. After what time, will the ball pass him going
                        downwards? How long after its release ,will the ball reach the ground?    (3M)
                    3.  Rahul puts a fresh egg into a beaker with water, and it sinks. Then he dissolved a lot
                        of salt in water and the egg began to rise and then floated. Why do you think the
                        egg starts floating? Share your views and support the activity performed  by Rahul
                        by giving a proper reason.                                                                                      (3M)
                 CASE BASED QUESTION
                 Q1.   Meenal’s teacher taught that class that every object in the universe attracts every
                 other object with a force, which is proportional to the product of their masses and inversely
                 proportional to the square of distance between them . This force is along the line, joining
                 the centers of two objects, as shown in the figure. Minal asked some questions from a
                 teacher .

                    A)  Why is  G called the universal constant ?
                    B)  What happens to the gravitational force between 2 objects if the masses of both
                        objects are tripled and the distance between them is halved ?
                    C)  What is the value of  G ’on moon and ‘g’ on moon?
                    D)  The ratio of gravitational force on Neptune to the gravitational force of Earth is 9 :8.
                        A child weighs 460 Newton on Earth. Calculate its weight on Neptune. (4M)
                 B.        We know that the earth attracts every object with a certain force, and this force
                 depends on the mass of the object and the acceleration due to gravity. The weight of an
                 object is the force with which it is attracted towards the earth .The SI  unit of weight is the
                 same as that of force that is Newton. The weight is a force acting vertically downwards,it
                 has Both magnitude and direction. We have learnt that the value of G is constant a given
                 place. Therefore, at a given place, the weight of an object is directly proportional to the
                 mass. Say m of the object, that is W proportional to m’. It is due to this reason that at a
                 given place, we can use the weight of an object as a measure of its mass.
                 a) Write any two factors on which weight of the object depends.
                 b) What is the direction of the weight of an object on earth?
                 c) Differentiate between mass and weight.
                 d) Will the weight of an object be lesser or more in Antarctica than its weight in Delhi . Give
                 a reason for your answer .                                                                                                       (4M)
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