Read the paragraph below and answer the questions from Q.29 to Q.32. You have learnt in Class VII that strong winds during a storm or a cyclone can blow away even the roof-tops. You also learnt that winds and cyclones are caused by the differences in air pressure. Is there any relation between pressure and force? Let us find out. Try to push a nail into a wooden plank by its head. Did you succeed? Try now to push the nail by the pointed end. Could you do it this time? Try cutting vegetables with a blunt knife and then with a sharp knife. Which is easier? Do you get the feeling that the area over which the force is applied (for example, the pointed end of the nail) plays a role in making these tasks easier? The force acting on a unit area of a surface is called pressure. Two rods of the same weight and equal length have different thickness. They are held vertically on the surface of sand as shown in the figure. Which one of them will sink move? Why? * 1 point Captionless Image (a) In Rod B area of contact is smaller, so will exert less pressure (b) In Rod A area of contact is smaller, so will exert more pressure (c) In Rod B area of contact is smaller, so will exert more pressure (d) In Rod B area of contact is smaller, so will exert equal pressure 30. Calculate the pressure produced by a force of 800 N acting on an area of 2.0 m2. * 1 point (a) 500 Pa (b) 450 Pa (c) 400 Pa (d) 200 Pa 31. Two women are of the same weight. One wears sandals with pointed heels while the other wears sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach? Give reason. * 1 point (a) women with a flat heel will be more comfortable, because of larger surface area (b) women wearing sandal with a pointed heel will be more comfortable (c) women with a flat heel will be more comfortable, because less surface area (d) women wearing with a pointed heel will be more comfortable, because of large surface area 32. The pressure of a gas contained in a cylinder with a movable piston is 300 Pa. The area of the piston is 0.5 m2. Calculate the force that is exerted on the piston. * 1 point (a) 50 N (b) 500 N (C) 1500 N (d) 150 N 33. Answer Q.33 to Q.36 based on the paragraph given. Have you ever seen a garbage dump where animals are eating garbage? In the process of eating the food waste they swallow materials like polythene bags and wrappers of food. Can you imagine the consequences? The plastic material chokes the respiratory system of these animals, or forms a lining in their stomachs and can be the cause of their death. The polybags carelessly thrown here and there are responsible for clogging the drains, too. Sometimes we are very careless and throw the wrappers of chips, biscuits and other eatables on the road or in parks or picnic places. The 5R Principle is - * 1 point Captionless Image (a) Reduce, Reuse, Recycle, Recover, Refuse (b) Remember, reduce, Recycle, Reset (c) Repeat, Rejoice, recycle, reduce (d) None of the above 34. Which of the following is Non-biodegradable waste? * 1 point (a) Woolen clothes (b) Plastic bag (c) Cotton cloth (d) Wood 35. Which of the following is a characteristic of plastics? * 1 point (a) Electrical conductors (b) Heat conductors (c) Biodegradable (d) Non-biodegradable 36. What are the consequences when animals eat the food waste from the garbage? * 1 point (a) Chokes the respiratory system (b) Forms a lining in the stomach (c) Can cause death of the animals (d) All of the above 37. Answer Q.37 to Q.40 based on the paragraph given. Take five 100 mL beakers and label them A, B, C, D and E. Take about50 mL of water in each beaker. Dissolve in each beaker a teaspoonful of each substance as indicated in the figure . Keep the beakers undisturbed for some time. What changes do you observe in the various beakers? You have read that one metal displaces another metal from its compound in aqueous solution. Complete the reaction- Copper sulphate + Zinc -------- _______ + ______ * 1 point Captionless Image (a) No reaction (b) Zinc sulphate + Copper (c) Zinc displaces copper (d) Both B and C
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Explanation:
- The relation between force and pressure is that pressure is equal to force applied per unit area.
- To push the nail into wooden plank with its head is tough because surface area is more and less pressure would be less, hence we have to put more pressure. Whereas it is easier to push nail with its pointed head as surface area is less and with more pressure it can be done. Blunt knife has more surface area than a sharp knife and hence we need more force to exert more pressure to cut vegetables.
- The force acting on a unit area of a surface is called pressure.
- (b) In Rod A area of contact is smaller, so will exert more pressure
- The pressure produced by a force of 800 N acting on an area of 2.0 m² = (c) 400 Pa, as pressure is equal to force per unit area.
- Which one would feel more comfortable while walking on a sandy beach (a) women with a flat heel will be more comfortable, because of larger surface area
- The force that is exerted on the piston: Force = Pressure × Area= 300 Pa× 0.5 m²= (d) 150 N
- The 5R Principle is: (a) Reduce, Reuse, Recycle, Recover, Refuse
- A characteristic of plastics: (d) Non-biodegradable
- The consequences when animals eat the food waste from the garbage: (d) All of the above
- Complete the reaction- (b) Zinc sulphate + Copper
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