1When an empty, tightly capped plastic bottle is pushed into water, do you feel that the bottle is being pushed upwards? Explain.
2When a plastic bottle is let go in the air it falls because of gravity, but why doesn't it sink when it is placed on the surface of the water?
3Doesn't gravity act on the bottle when it is placed in water?
4What happens when the empty bottle is filled with water and then placed in the bucket again?
5When a bucket submerged in water is pulled out with a rope, what is the difference between the force required to pull it while it is in the water and after it comes out into the air?
6A stone is hung from a spring balance and weighed first in air and then submerged in water. Is the weight in air equal to the weight in water?
7Define upthrust. What is its SI unit?
8Explain why the direction of upthrust is always upward.
9Differentiate between real weight and apparent weight.
10A stone weighs 8 N in air and 5 N when it is completely immersed in water. Calculate the upthrust on it.
11Why is it easier to lift a friend in a swimming pool than on land?
12The upthrust of air on a bucket can be ignored, but the upthrust of air on an aeroplane cannot. Why?