Page 123 - Understanding NCERT Science 09

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/s , find the maximum height
2
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
24
Sun, given that the mass of the earth = 6 × 10 kg and of the
Sun = 2 × 10 30 kg. The average distance between the two is
11
1.5 × 10 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 cm . If the density of
3
water is 1 g cm , will the substance float or sink?
–3
3
22. The volume of a 500 g sealed packet is 350 cm . Will the
packet float or sink in water if the density of water is 1 g
–3
cm ? What will be the mass of the water displaced by this
packet?

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