Force and pressure Worksheet-12

Force and pressure Worksheet-12

41. Why does a boat come to rest when we stop rowing it?

42. What type of force exists between a magnet and iron piece and between two magnets?

43. What is meant by electrostatic force? Is it a contact force or a non-contact force?

44. Define pressure and give its SI unit.

45. Do we feel the effect of atmospheric pressure? Why?

46. Define Pressure. Write the relation between pressure force and area. Name the instrument used to measure atmospheric pressure.

47. (a) A can filled with water, is heated so that water boils. Now seal the mouth with air-tight cap. Let the can cool. Its sides get deformed. Explain why?

(b) Why are astronauts made to wear specially made suits to go into space?

48. We hammer the broader side of a nail and not its sharp end to put it in wood. Why?

49. Why is it difficult to cut vegetables with a blunt knife?

50. Trucks intended to carry heavy loads have eight tyres instead of four tyres. Why?

51. Give reasons for the following :

(a) The skiers use flat and broad skis

(b) Deep sea divers wear special suits.

52. How does the medicine enter a dropper?

53. You are given rubber sucker with a hook. Can you use it for hanging articles? Explain how? Give the principle involved.

54. A boy throws a ball upwards, but it comes down after sometime. Why? Which force is acting on the ball? What type of force is it?

55. Why do we observe sparks coming out from a synthetic shirt when we take it off our body?

Which force pulls the iron nails towards a magnet?

Answer:

41. The boat comes to rest when we stop rowing it due to the force of friction acting between the surface of water and the boat.

42. Non-contact force exists between two magnets and an iron piece and a magnet.

43. The force exerted by a charged body is known as electrostatic force. It is a non-contact force.

44. Pressure is force per unit area. SI unit of pressure is Newton per (metre)² or Nm^–2.

45. No, we do not feel the pressure of the atmosphere because air is present everywhere. Also the pressure of air inside our body is same as that of the atmosphere.

46. Pressure is force per unit area.

Barometer is used to measure atmospheric pressure.

47. (a) There is no pressure inside the can as there is vacuum but the atmospheric pressure is acting from outside. Therefore, it gets crushed or deformed.

(b) In space, atmospheric pressure is extremely less. The pressure inside our body is higher. Therefore, astronauts wear specially made suits.

48. In this case, the force would be acting in less area, therefore, it would exert maximum pressure on the nail. As a result, the sharp end of the nail could easily pierce in the wood.

49. Pressure is inversely proportional to area. The area of the blunt knife is more and therefore, the effect of the force is less. Therefore, more force has to be applied.

50. Trucks intended to carry heavy loads have eight tyres, so as to increase the area of contact with the road. Since pressure is inversely proportional to area, less pressure is applied on the road and that leads to smooth movement.

51. (a) The skiers used flat and broad skis to ski on the snow. The larger surface of skis reduces pressure on snow and helps them to slide instead of sinking.

(b) Deep sea divers wear special suits, because the pressure of water increases with depth. The increased pressure may hurt the body of divers.

52. When the dropper is pressed, the air inside the dropper is driven out. The pressure inside the dropper decreases and the medicine rushes inside the dropper.

53. Yes. On pressing the sucker, the air between the cup and the surface escapes out. The pressure inside is reduced, but the atmospheric pressure is more. Therefore, the sucker remains stuck to hold articles.

54. The ball comes down to the force of gravity exerted by the earth. Force of gravity is a non-contact force and it acts on a body even through the two are not in contact with each other.

55. The sparks come out from a synthetic shirt due to the electrostatic charge on it.

Magnetic force.