Exercises:
A. Multiple Choice Questions
Answers:
1. c
2. c
3. c
4. a
5. a
6. b
7. d
B. Complete the sentence:
Answers:
1. c
2. e
3. d
4. a
5. b
C. Fill in the Blanks:
1. weight
2. volumes
3. density
4. 1
5. weight of the water displaced
D. Answer the following questions:
Ans: 1. Density is defined as the weight of unit volume of a substance. Hence it tells us how closely the molecules of the substance are packed. The greater the density, the more closely the molecules are packed. If the object is denser than water, it sinks in water. If it is less dense, it floats.
Ans: 2. Archimedes’ principle states that when an object is immersed in water, the upthrust is equal to the weight of water displaced by the object.
Ans: 3.
According to the Archimedes’ principle, the rules for floating and sinking are:
(i) If the weight of an object is more than the upthrust, the object sinks in water.
(ii) If the upthrust is more than the weight of an object, the object floats in water.
Ans: 4.
Even though the iron used for making a boat sinks in water, the boat floats in water due to its shape. A boat is hollow. When the boat is in water, the entire volume of the boat, including the hollow portion displaces water to make space for itself. This volume of water is more than the volume of iron used for making the boat. According to Archimedes’ principle, the upthrust is more than the weight of the boat and hence it floats in water.
Ans: 5.
When an object is immersed in water it displaces some water. The weight of water displaced equals the upthrust experienced by the object. Hence the downward force experienced by the object will be lesser by this upthrust. Therefore, the weight of an object in water = weight in air−upthrust (that is, weight of water displaced).
Higher-order Thinking Skills
Ice floats on water. Hence the density of water as a solid is lesser than that as a liquid.