## Density, Buoyancy and Archimedes' Principle (Assignment)

1. When we stand on loose sand, our feet go deep into the sand. But when we lie down on the sand our body does not go that deep in the sand. Why ?

2. Define relative density of a substance. Relative density of silver is 10.8. The density of water is 1000 kg/m³ What is the density of silver in SI units?

3. A cork floats in water, while the iron nail sinks. Give reason. (2)

4. State Archimedes' Principle. Based on this principle, write its two applications. (2)

5. (i) Define pressure. (2)
(ii) Why is it easy to walk on sand with flat shoes, than with high heel shoes?

6. (i) Define buoyant force. (2)
(ii) Mention any two factors affecting the buoyant force.

7. Loaded test-tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less ? Explain. (2)

8. If two equal weights of unequal volumes are balanced in air, what will happen when these are completely dipped in water? (2)

9. Give reason why, a block of plastic when released under water comes up to the surface of water.(1)

10. A steel needle sinks in water but a steel ship floats. Explain how. (2)

11. The volume of 40 g of a solid is 15 cm3. If the density of water is 1g/cm3, will the solid float or sink? Why? (2)

12. What happens when : (2)
(a) Buoyant Force exerted by the fluid is less than the weight of the body ?
(b) Buoyant Force exerted by the fluid is equal to the weight of the body ?

13. What is Relative Density ? The relative density of a substance is greater than, what does it signify ? (2)

14. (a) Name the forces acting on a body. When it is fully or partially immersed in a liquid.  (2)
(b) Briefly explain, why some objects float and some sink ?

15. A dining hall has dimension 50 m x 15 m x 3.5 m. Calculate the mass of air in the hall.  (2)
(Given, density of air = 1.30 kg/m³)

16. Relative densities of two substances A and B are 2.5 and 0.9 respectively. Find densities of A and B. Also find whether they will sink or float in water. (Density of water = 1000 kg/m³).

17. (a) List two factors on which buoyant force depends.
(b) Find pressure, when a thrust of 20 N is applied on a surface area of 10 cm2.

18. (a) Explain why a truck or a motor bus has much wider tyres? (2)
(b) Why do we feel lighter when we swim?

19. If relative density of aluminium is 2.7 and density of water is 1000 kg/m³. What is the density of aluminium in SI unit?

20. Explain why wide sleepers are placed below railway lines? (1)

21. The volume of a solid block is 300 cm³, find the mass of water displaced when it is immersed in water ? (Density of water is 1 g/cm³) (2)

22. Give reasons: (2)
a. It is easier to lift a heavy stone under water.
b. A block of plastic released under water come up to the surface of water.

23. You have a bag of cotton and an iron bar, each indicating a mass of a 100 kg when measured on a weighing machine. In reality, one is heavier than the other. Can you say which one is heavier and why? (2)

24. Account for the statement : "Camel walks easily on sand but it is difficult for a man to walk on sand though a camel is much heavier than a man". (2)

25. A piece of stone is tied at one end of a rubber string and holding from other end, it is allowed to immersed partially then fully into water. What difference if any, you will observe, and why? (2)

26. If we lift a body of mass 70 g vertically upwards 10 m then calculate the force required to lift the body   (g = 10ms⁻²)
(1)
27. A solid object of mass 50g and volume 100 cm³ is put in water. Will the object float or sink ? Give reasons for your answer. (2)

28. Name the instrument used to determine the density of liquids in which balance and graduated cylinder are not required. Why this instrument is made heavy near the bottom? (2)

29. A sphere of mass 5 kg and volume 2.2 x 10-4 m³ is completely immersed in water. Find the buoyant force exerted by water on the sphere. Density of water =1000kg/m³ (Given : g = 9.8ms⁻²) (2)

30. A ship is loaded in sea water to maximum capacity. What will happen if this ship is moved to river water? Why? (2)

31. Why is it easier to swim in sea water than in river water ? (2)

32. Differentiate between density and relative density? (2)

33. Why is a bucket of water lighter when in water than when it is taken out of water.  (2)

34. (a) Differentiate between up thrust and weight (1)
(b) When does an object float or sink. (1)

35. A sealed can of mass 600 g has a volume of 500 cm³. Will this can sink or float in water ? (2)
[Density of water is 1g/cm³] Why?

36. What is Thrust? Why do buildings have wide foundation? (2)

37. (a) Define Buoyancy. (3)
(b) A solid body of mass 150 g occupies 60 cm3 volume. Will the solid sink or float? Given density of water is 1 g/cm³.

38. You find your mass to be 52 kg on a weighing machine. Whether your mass is more or less than 52 kg ? Comment with reasons. (2)

39. Explain the factors which determine wheter an object floats or sinks when placed on the surface of water. (2)

40. Two blocks, one of iron and other of wood are immersed in water at same depth. Which one will come upward? Why(2)

41. (a) Define relative density (2)
(b) If the relative density of a substance is less than 1, will it float or sink in water support your answer (Density of water =1000 Kg/m³)

42. (a) Name the force experienced by an object in a fluid when immersed in it. What is its direction ?
(b) State the physical expression relating weight of the body in the liquid, actual weight of the body in air and the weight of the liquid displaced by the body.

43. State Archimedes principle. Give any two examples where Archimedes principle is applied.

44. The mass of an empty 40 litre petrol tank of a vehicle is 8.0 kg. What will be its mass when filled completely with a fuel of density 700 kg/m³.

45. Lead has greater density than iron and both are denser than water. Is the buoyant force on a lead object greater than, or lesser than or equal to the buoyant force on an iron object of the same volume ? Explain your answer giving reason. (2)

46. The wheels of an army tank rest on a steel belt, Give reason. (2)

47.  (a) A floating boat displaces water weighing 6000 N.
(i) What is the buoyant force on the boat.
(ii) What is the weight of the boat.
(b) What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid.

48. (a) Why does a block of wood held under water rise to the surface when released? (2)
(b) An object of weight 200 N is floating in a liquid. What is the magnitude of buoyant force acting on it?  