## Samacheer Kalvi 9th Term III Science Book Back Question and Answers – Unit 1:

Samacheer Kalvi 9th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2021 to 2022 Book Back Question & Answer solutions available for both English and Tamil Medium. Class 9 Science Book Term 3 Unit 1 – Fluids Answers/Solutions are provided on this page. 9th Std Science Book is of Term 1st, 2nd, 3rd, and consists of 9 Units in each Term. All 9 Units of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

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### Samacheer Kalvi 9th Science Book Back Unit 1 Term 3 Solutions Guide PDF:

Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

### 1. Choose the correct answer:

1. The size of an air bubble rising up in the water
a) decreases                 b) increases
c) remains the same  d) may increase or decrease

2. clouds float in the atmosphere because of their low
a) density b) pressure
c) velocity d) mass

3. In a pressure cooker, the food is cooked faster because
a) increased pressure lowers the boiling point
b) increased pressure raises the boiling point
c) decreased pressure raises the boiling point
d) increased pressure lowers the melting point.

4. An empty plastic bottle closed with an airtight stopper is pushed down into a bucket filled with water. As the bottle is pushed down, there is an increasing force on the bottom as shown in the graph. This is because

a) more volume of liquid is displaced
b) more weight of the liquid is displaced.
c) pressure increases with depth
d) all the above

### II. Fill in the blanks:

1. In a fluid, buoyant force exists because the pressure at the bottom of an object is greater than the pressure at the top.
2. The weight of the body immersed in a liquid appears to be less than the actual weight.
3. The instrument used to measure atmospheric pressure is a barometer.
4. The magnitude of buoyant force acting on an object immersed in a liquid depends on the density of the liquid.
5. A drinking straw works on the existence of atmospheric pressure.

### III. True or False:

1. The Weight of fluid displaced determines the buoyant force on an object. – True
2. The shape of an object helps to determine whether the object ill float. – True
3. The foundations of high-rise buildings are kept wide so that they may exert more pressure on the ground. – False
4. Archimedes principle can also be applied to gases. – True
5. Hydraulic press is used in the extraction of oil form oil seeds. – False

### IV. Match the following:

1. Density            a) hpg
2. 1 gwt                 b) Milk
3. Pascal’s law    c) 𝑚𝑎𝑠𝑠 𝑣o𝑙𝑢𝑚e
4. Pressure exerted by a fluid d) pressure
5. Lactometer     e) 980 dyne

Ans: 1– c; 2- e; 3-d; 4-a; 5-b

### V. Assertion and Reason:

Directions: In each of the following questions, a statement of Assertion (A) is given followed by a corresponding statement of Reason (R) just below it. Of the statements, mark the correct answer as
a) If both assertion and reason are true and reason is the correct explanation of assertion.
b) If both assertion and reason are true but reason is not the correct explanation of assertion.
c) If assertion is true but reason is false.
d) If assertion is false but reason is true.

1. Assertion: To float, body must displace liquid whose weight is equal to the actual weight.
Reason: The body will experience no net downward force in that case.
Ans: a) If both assertion and reason are true and reason is the correct explanation of the assertion.

2. Assertion: Pascal’s law is the working principle of a hydraulic lift.
Reason: Pressure is thrust per unit area.
Ans: b) If both assertion and reason are true but reason is not the correct explanation of assertion.

3. Assertion: The force acting on the surface of liquid at rest, under gravity, in a container is always horizontal.
Reason: The forces acting on a fluid at rest have to be normal to the surface.
Ans: d) If assertion is false but reason is true.

4. Assertion: A sleeping mattress is so designed that when you lie on it, a large area of your body comes in the contact.
Reason: This reduces the pressure on the body and sleeping becomes comfortable.
Ans: a) If both assertion and reason are true and reason is the correct explanation of assertion.

5. Assertion: Wide wooden sleepers are kept below railway lines to reduce pressure on the railway tracks and prevent them from sinking in the ground.
Reason: Pressure is directly proportional to the area in which it is acting.
Ans: c) If assertion is true but reason is false.

### VI. Short Questions & Answers:

1. On what factors does the pressure exerted by the liquid depend on?

Pressure exerted by a liquid at a point is determined by (i) depth (h) (ii) density of the liquid (p) (iii) acceleration due to gravity (g).

2. Why does a helium balloon float in air?
Hydrogen, helium and hot air are much less dense than ordinary air. This gives them buoyancy to rise and float in air.

3. Why is it easy to swim in river water than in sea water?
Salt water provides more buoyant force than fresh water because buoyant force depends as much on the density of fluids as on the volume displaces. So it is easier to swim in river water than in sea water.

4. What is meant by atmospheric pressure?
The pressure exerted by a layer of air upto certain height (nearly 300 km) around the earth is called the atmospheric pressure.

5. Sate Pascal’s law.
The external pressure applied on an incompressible liquid is transmitted uniformly throughout the liquid.
Pascal’s law states that an increase in pressure at any point inside a liquid at rest is transmitted equality
and without any change, in all directions to every other point in the liquid.

6. How does an object’s density determine whether the object will sink or float in water?
Whether an object will sink or float in a liquid is determined by the density of the object compared to the density of the liquid. If the density of a substance is less than the density of the liquid it will float. For example a piece of wood which is less dense than water will float on it. Any substance having more density than water (for example, a stone) will sink into water.

7. State the laws of flotation.
Laws of flotation are:
a) The weight of a floating body is a fluid is equal to the weight of the fluid displaced by the body.
b) The centre of gravity of the floating body and the centre of buoyancy are in the same vertical line. The point through which the force of buoyancy is supposed to act is known as centre of buoyancy.

8. How does the fish manage to rise up and move down in water?
Fish has an internal swim bladder which is fixed with gas. When it needs to ride or descend, it changes the volume and its density.

9. If you put one ice cube in a glass of water and another in a glass of alcohol, what would you observe? Explain your observation.
If one ice cube is put in a glass of water, it will float on the surface of water because the density of ice cube is less than that of water. But if it is put in a glass of alcohol, it will sink into it because the density of ice cube is greater than that of alcohol.

10. You have a bag of cotton and an iron bar, each indicating a mass of 100 kg when measured on a weighing machine. In reality, one is heavier than other. Can you say which one is heavier and why?
In reality, a bag of cotton is heavier. The volume of 100 kg of iron bar is less than that of 100 kg of cotton bag. So the up thrust for cotton bag when weighing in air medium is higher than that of the iron bar.

11. Why does a boat with a hole in the bottom would eventually sink?
The shape of the boat is constructed in such a way that the weight of the water displaced is equal to the weight of the boat. In a boat with a hole in the bottom, water enters into the boat and as a result the weight increases. When the weight of the boat is greater than the water displaced by the boat, the boat sinks into the water.

### VII. Comprehensive type Questions:

1. While passing nearby a pond, some students saw a drowning man screaming for help. They altered another passerby, who immediately threw an inflated rubber tube in the pond. The man was saved. Respond to the given questions using the information provided above.
a) Why did the passerby use inflated rubber tube to save the drowning man?
The inflated rubber tube will not sink into the water even if it is loaded heavily. So the passerby used inflated rubber tube to save the drowning man.

b) Write the principle involved herein.
The density of air is less than the density of water. So the inflated rubber tube floats.

c) Which qualities shown by the students and the passerby do you identify that helped in saving the drowning man.
The students had the presence of mind to call out for help. The passerby had the scientific knowledge that a tube filled with air will always float and prevent the man from drowning.

2. A balloon displaces air and it results in buoyant force. This buoyant force is more than the weight of the balloon and hence the balloon moves up.
a) As the balloon moves up what happens to the density it?
As the balloon moves up, the density of air decreases.

b) Write the condition for floating of balloon.
The weight of the floating balloon in the air is equal to the weight of the air displaced by the floating balloon.

c) Buoyant force depends on the density of
The buoyant force depends on the density of fluids.