Pressure, Winds, Storms, and Cyclones — Hard

Q1. An elephant of weight 20000 N stands on all four feet. If the area under each foot is 0.25 m^2, the pressure exerted by the elephant on the ground is

• A. 5000 N/m^2
• B. 20000 N/m^2
• C. 1250 N/m^2
• D. 80000 N/m^2

Q2. Boat A has base area 7 m^2 with 5 persons in it; Boat B has base area 3.5 m^2 with 3 persons. If each person has a weight of 700 N, which boat exerts more pressure on its base and by how much?

• A. Boat A by 100 N/m^2
• B. Boat B by 100 N/m^2
• C. Both exert the same pressure
• D. Boat A by 200 N/m^2

Q3. Two vessels A and B contain water up to the same level. Vessel A is narrow and B is wide (Fig. 6.22). If P_A, P_B are the pressures at the bottom and F_A, F_B are the forces exerted by water at the bottom, the correct relation is

• A. P_A = P_B, F_A = F_B
• B. P_A = P_B, F_A < F_B
• C. P_A < P_B, F_A = F_B
• D. P_A > P_B, F_A > F_B

Q4. Fig. 6.23(a) shows a boy lying horizontally on a loose sand bed and Fig. 6.23(b) shows the same boy standing vertically on it. In which case does the boy sink more, and why?

• A. While lying, because his whole weight acts at one end
• B. While standing, because the same weight acts on a much smaller area (feet) and produces a higher pressure on the sand
• C. Sinking is the same in both cases because his weight does not change
• D. While standing, because gravity is stronger on a standing body

Q5. Would lightning occur if air and clouds were good conductors of electricity? Choose the best reasoning.

• A. Yes, lightning would actually become more violent because conductors carry more current
• B. Yes, because conductors store more static charge than insulators
• C. No, because then opposite charges would meet continuously and there would be no sudden build-up to break down the insulating property of air
• D. No, because warm air would no longer rise from heated land

Q6. Consider the following statements about cyclone formation over warm ocean waters: I. As moist air rises, water vapour condenses to form raindrops and heat is released back into the atmosphere. II. The released heat warms the ascending air further, leading to even lower pressure at the centre. III. The Sun's heat directly creates the spinning motion of a cyclone. Which of the above statements are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q7. Holes are often deliberately left in large banners and hoardings put up along roads. The best reason is

• A. To allow rainwater to pass through and avoid heavy dripping
• B. To make the banner look more attractive against the sky
• C. To let high-speed winds pass through, reducing the pressure difference between the two sides and the chance of the banner being blown away
• D. To let birds nest inside the banner

Q8. Water is filled to the same height in a bottle that has two identical balloons fitted at side holes — balloon A on the narrow side and balloon B on the broader side (Fig. 6.24). Which is correct about their bulging?

• A. Only A will bulge because it is on the narrower side
• B. Only B will bulge because it is on the broader side
• C. Both will bulge, but A will bulge much more than B
• D. Both will bulge and they will bulge to the same extent

Q9. Fig. 6.25 shows trees along a sea coast in a summer afternoon, bent from side A towards side B. Which side is land, and why?

• A. A is land; the land heats faster than the sea during the day, warm air over A rises and cooler air from the sea (B) blows towards A, bending the trees from A towards B
• B. B is land; the land heats faster than the sea during the day, warm air over B rises and cooler air from the sea (A) blows towards B, bending the trees from A towards B
• C. A is land; the wind always blows from land to sea during the day
• D. Neither side is land; the trees are bent only because of the rotation of the Earth

Q10. Arrange the following events in the correct order during the formation of a thunderstorm: I. Warm, moist air rises and creates a low-pressure area. II. The rising air cools and moisture in it condenses to form water droplets, creating clouds. III. Cooler air from surrounding high-pressure regions rushes in to take its place. Which is the correct chronological order?

• A. II, I, III
• B. I, III, II
• C. III, I, II
• D. I, II, III

Q11. An overhead water tank is placed on the roof of a three-storeyed building. A friend lives on the first floor and you live on the second floor. Whose tap will give a more powerful stream of water?

• A. Your friend on the first floor, because the height of the water column above his tap is greater
• B. You on the second floor, because the tap is closer to the tank and the column height is smaller
• C. Both will receive equally powerful streams since the same tank supplies both
• D. Neither will get water because the tank is too high

Q12. Assertion (A): During a thunderstorm, trees and buildings on the ground often become positively charged. Reason (R): The negatively charged lower part of a thundercloud, when it comes close to the ground, induces a positive charge on the ground and on nearby tall objects. Choose the correct option

• A. Both A and R are true, and R is the correct explanation of A
• B. Both A and R are true, but R is NOT the correct explanation of A
• C. A is true, R is false
• D. A is false, R is true

Q13. In Activity 6.3, a paper plate is covered first with a folded chart paper sheet (small area) and then with an unfolded chart paper sheet (large area), and lifted using a stick each time. Which observation is correct, and what does it prove?

• A. Lifting is easier with the unfolded sheet; this proves that the weight of the covering sheet has changed
• B. Lifting needs more effort with the unfolded sheet; this proves that air exerts pressure on the covering sheet, and that the required force increases with the covered area
• C. Lifting needs the same effort in both cases; this proves that atmospheric pressure does not depend on area
• D. Lifting needs more effort with the folded sheet; this proves that folded paper is heavier than unfolded paper

Q14. Consider these statements about the effects of a cyclone reaching a coast: I. Strong cyclonic winds push ocean water towards the shore, creating a wall of water that can be 3 to 12 metres high. II. Seawater rushing inland can contaminate drinking water sources and reduce soil fertility because of its salt. III. Cyclones always increase the fertility of farmland by depositing fresh river sediments. Which statements are correct?

• A. I and III only
• B. I and II only
• C. II and III only
• D. All three

Q15. The practical unit of air pressure is millibar (mb), where 1 mb = 100 Pa. An air pressure reading of 1013 mb is approximately equivalent to

• A. 101300 Pa
• B. 1013 Pa
• C. 10130 Pa
• D. 10.13 Pa