Gravitation Worksheet-14

Gravitation Worksheet-14

31. (a) What are fluids? Name two common fluids.

(b) State Archimedes’ principle.

32. A piece of steel has a volume of 12 cm², and a mass of 96 g. What is its density :

(i) in g/cm³?

(ii) in kg/m³?

33. An elephant weighting 40,000 N stands on one foot of area 1000 cm² whereas a girl weighing 400 N is standing on one heel of area 1 cm².

Which of the two, elephant or girl, exerts a larger force on the ground and by how much?

34. An elephant weighting 40,000 N stands on one foot of area 1000 cm² whereas a girl weighing 400 N is standing on one heel of area 1 cm².

What pressure is exerted on the ground by the girl standing on one heel?

35. An elephant weighting 40,000 N stands on one foot of area 1000 cm² whereas a girl weighing 400 N is standing on one heel of area 1 cm².

 Which of the two exerts larger pressure on the ground : elephant or girl ?

36. An elephant weighting 40,000 N stands on one foot of area 1000 cm² whereas a girl weighing 400 N is standing on one heel of area 1 cm².

What is the ratio of pressure exerted by the girl to the pressure exerted by the elephant ?

37. If two equal weights of unequal volumes are balanced in air, what will happen when they are completely dipped in water? why?

38. Two different bodies are completely immersed in water and undergo the same loss in weight. Is it necessary that their weights in air should also be the same? Explain.

39. A body floats in kerosene of density 0.8 × 10³ kg/m³ up to a certain mark. If the same body is placed in water of density 1.0 × 10³ kg/m³, will it sink more or less ? Give reason for your answer.

40. Giving reasons state the reading on a spring balance when it is attached to a floating block of wood which weighs 50 g in air.

41. If a fresh egg is put into a beaker filled with water, it sinks. On dissolving a lot of salt in the water, the egg begins to rise and then floats. Why ?

42. A beaker full of water is suspended from a spring balance. Will the reading of the balance change :

(a) if a cork is placed in water ?

(b) if a piece of heavy metal is placed in it ?

43. When a golf ball is lowered into a measuring cylinder containing water, the water level rises by 30 cm³ when the ball is completely submerged. If the mass of ball in air is 33 g, find its density.

44. A boy gets into a floating boat.

What happens to the boat ?

45. A boy gets into a floating boat.

What happens to the weight of water displaced ?

46. A (1/2) kg sheet of tin sinks in water but if the same sheet is converted into a box, it floats. Why ?

Answer:

31. –

32. (i) 8 b/cm³ (ii) 8000 kg/m³

33. Elephant has a larger weight of 40000 N , therefore, elephant exerts a larger force on the ground ; Elephant exerts a larger force on the ground by 40000 N – 400 N = 39600 N

34. 4000,000 N/m²

35. Girl

36. 4000,000 : 400,000 = 10 : 1 ; The pressure exerted by girl is 10 times greater than that exerted by the elephant

37. The two equal weights of unequal volumes will get unbalanced when they are completely immersed in water ; This is because due to their unequal volumes, they will displace unequal volumes of water and hence suffer unequal loss in weight when completely dipped in water.

38. No, it is not necessary that their weights in air should also be the same; This is because the two bodies have undergone the same loss in weight on completely immersing in water due to their equal volumes and not because of their equal weights, so they may have different weights in air

39. The body will sink less in water ; This is because the density of water (1 × 10³ kg/m³) is more than the density of kerosene (0.8 × 10³ kg/m³) due to which water will exert a greater ‘upward’ buoyant force on the body

40. The reading on spring balance will be 0 (zero) ; This is because the weight of floating block of wood is fully supported by the liquid in which it is floating and hence it does not exert any force on the spring balance

41. When a lot of salt is dissolved in water, then the density of salt solution becomes much more than pure water. Due to its much higher density, the salt solution exerts a greater ‘upward’ buoyant force on the egg making it rise and then float.

42. (a) the reading of spring balance will not change if a cork is placed in water because cork, being lighter than water, floats in water

(b) The reading of spring balance will change if a piece of heavy metal is placed in water because heavy metal, being denser than water, sinks in water

43. 1.1 g/cm³

44. The boat sinks a little more in water, that is, the boat floats lower in water

45. The weight of water displaced (by the submerged part of boat) increases

46. The sheet of tin sinks in water because the density of tin is higher than that of water ; When the sheet of tin is converted into a box then due to the trapping of lot of ‘light’ air in the box  the average density of box  made of tin sheet becomes lower than that of water so  it floats on water.