Samacheer Kalvi 8th Science Unit 2 Answers

Samacheer Kalvi 8th Science Unit 2 Book Back Answers:

Samacheer Kalvi 8th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 8 New Syllabus 2021 to 2022 Book Back Question & Answer available for both English and Tamil Mediums. Class 8th Science Book Unit 2 – Force and Pressure Answers/Solutions are provided on this page. 8th Std Science Book consists of 23 units, All Science Book Back One, and Two Mark Solutions are given below.

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Samacheer Kalvi 8th Science Book Back Solutions PDF:

8th Science Subject 1 Mark and 2 Mark Solutions 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. Samacheer Kalvi 8th Science Unit 2 Answers are given below.

Science Book Back Answers

Unit 2 – Force and Pressure

I. Choose the best answer

1. If we apply a force against the direction of motion of a body, then the body will –
(a) Stop moving
(b) Move with an increased speed
(c) Move with a decreased speed
(d) Move in a different direction
Answer:
(a) stop moving

2. Pressure exerted by a liquid is increased by –
(a) The density of the liquid
(b) The height of the liquid column
(c) Both (a) & (b)
(d) None of the above
Answer:
(c) Both (a) & (b)

3. Unit of pressure is –
(a) Pascal
(b) N m^-2
(c) Poise
(d) Both (a) & (b)
Answer:
(d) Both (a) & (b)]

4. The value of the atmospheric pressure at sea level is –
(a) 76 cm of mercury column
(b) 760 cm of mercury column
(c) 176 cm of mercury column
(d) 7.6 cm of mercury column
Answer:
(a) 76 cm of mercury column

5. Pascal’s law is used in –
(a) Hydraulic lift
(b) Brake system
(c) Pressing heavy bundles
(d) All the above
Answer:
(d) All the above

6. Which of the following liquids has more viscosity?
(a) Grease
(b) Water
(c) Coconut oil
(d) Ghee
Answer:
(a) Grease

7. The unit of viscosity is –
(a) N m²
(b) Poise
(c) kg m s^-1
(d) No unit
Answer:
(b) poise

II. Fill in the blanks

The pressure of a liquid column …………….. with the depth of the column.
Hydraulic lift works under the principle of ………………
The property of …………… of a liquid surface enables the water droplets to move upward in plants.
A simple barometer was first constructed by ……………..

Answer:

Increases
Pascal’s Law
Surface tension
Torricelli

III. State whether the following statements are true or false

1. Force acting on a given area is called pressure.
Answer:
True

2. A moving body comes to rest due to friction alone.
Answer:
True

3. A body will sink if the weight of the body is greater than the buoyant force.
Answer:
True

4. One atmosphere is equivalent to 1,00,000 newton force acting on one square metre.
Answer:
True

5. Rolling friction is slightly greater than the sliding friction.
Answer:
False
Correct statement:
Rolling friction is slightly lesser than the sliding friction.

6. Friction is the only reason for the loss of energy.
Answer:
True

7. Liquid pressure decreases with the decrease of depth.
Answer:
True

8. Viscosity depends on the pressure of a liquid.
Answer:
True

IV. Match the following.

Answer:

i – e; ii. c; iii. b; iv. a; v. d

Answer:

i. b; ii. d; iii. e; iv. a; v. c

V. Analogy

1. Knot in a thread : ______ friction :: ball bearing : friction ______
Answer:
Rolling, Static.

2. Downward force : weight :: Upward force offered by liquid : ______
Answer:
Buoyant force.

VI. Numerical Problems:

1. A stone weighs 500 N. Calculate the pressure exerted by it if it makes a contact with a surface of area 25 cm2.
Answer:
Given : Weight of a stone F = 500 No
Area A = 25 cm² = 25 x 10^-4 m²
To find : Pressure P = ?
Formula :

Solution:
Pressure P = 20 x 10⁴N/m² (or) 20 x 10⁴ Pa

VII. Consider the statements given below and choose the correct option.

Mark the correct choice as :
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.

1. Assertion: Sharp knives are used to cut the vegetables.
Reason: Sharp edges exert more pressure.
Answer:
(a) Both assertion and reason are true and the reason is the correct explanation of the assertion

2. Assertion: Broad straps are used in bags.
Reason: Broad straps last for long.
Answer:
(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion
Correct explanation:
The weight of the bags falls on larger area of shoulder. So lesser pressure is produced.

3. Assertion: Water strider slides easily on the surface of water.
Reason: Water strider experiences less buoyant force.
a. Both assertion and reason are true and reason is the correct explanation of assertion.
b. Both assertion and reason are true, but reason is not the correct explanation of assertion.
c. Assertion is true, but reason is false.
d. Both assertion and reason are false.

Answer:
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion
Correct explanation :
It is due to the surface tension of water.

VIII. Answer very briefly.

1. Give two examples to verify that a force changes the shape of a body.
Answer:
Force can change the static condition of a body.

If you squeeze a sponge, its shape changes.
If you pull a rubber band, it becomes longer.

2. Give two examples to verify that a force tends to change the static condition of a body.
Answer:
Force can change the static condition of a body.

A rest rubber ball begins to move, when a force applied on it.
Player applies a force on the stationary football while taking a penalty kick is football match. The force applied by player makes the football move towards the goal.

3. What do you feel when you touch a nail immediately after it is hammered into a wooden plank? Why?
Answer:
The nail becomes hot due to friction. Friction changes kinetic energy to heat.

4. How does the friction arise between the surfaces of two bodies in relative motion?
Answer:
The force of friction is arised by the interlocking of the irregularities of the two surfaces.

5. Name two instruments, which help to measure the pressure of a fluid.
Answer:

Manometer
Pressure gauge.

6. Define one atmosphere.
Answer:
The pressure exerted by this mercury column is considered as the pressure of magnitude ‘one atmosphere’ (1 atm).

7. Why are heavy bags provided with broad straps?
Answer:
Broader straps are provided on a back – pack for giving less pressure on the shoulders by providing a larger area of contact with the shoulder.

8. How does surface tension help a plant?
Answer:
Water molecules rise up due to surface tension. Xylem tissues are very narrow vessels present in plants. Water molecules are absorbed by the roots and these vessels help the water to rise upward due to “capillarity action” which is caused by the surface tension of water.

9. Which has greater viscosity, oil or honey? Why?
Answer:
Honey has greater viscosity.
Reason : Thicker liquids are more viscous than thinner liquids. As honey has greater viscosity, more frictional force will be acting on it.

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22 Apr 2022