CBSE Class 8 Science Force and Pressure Assignment

Question. A car accelerates on a horizontal road due to the force exerted by:
(A) the engine of the ear
(B) the driver of the car
(C) the earth
(D) the road

Answer: D

Question. While walking on ice, one should take small steps to avoid slipping. This is because smaller steps ensure:
(A) larger friction
(B) smaller friction
(C) larger normal force
(D) smaller normal force

Answer: D

Question. A force is applied to an object in the direction of its motion. The speed of object will
(A) increase
(B) decrease
(C) can't say
(D) remain unchanged

Answer: A

Question. Friction can be increased by:
(A) making the surfaces rough
(B) using dry surfaces
(C) increasing the weight
(D) all of the above

Answer: D

Question. Which of the following is a non contact force?
(A) muscular
(B) electrostatic attraction
(C) elastic spring force
(D) friction force

Answer: B

Question. If no force acts on a body it will .....................
(A) change shape
(B) move with increased speed
(C) either remain in rest or move in a straight line
(D) break up

Answer: C

Question. The force of friction between two bodies is:
(A) parallel to contact surface
(B) perpendicular to contact surface
(C) inclined to contact surface
(D) a non contact force

Answer: A

Question. In football, a goal keeper stops a ball. This is due to:
(A) friction between the ball and hand of goal keeper
(B) decrease in speed of ball due to air resistance
(C) application of force by goal keeper
(D) all of the above

Answer: C

Question. Which of the following action describes pushing by a body?
(A) kicking
(B) lifting
(C) picking
(D) opening

Answer: A

Question. Which of the following example describes change of shape by applying force?
(A) kicking a ball to move faster
(B) switching on a fan to rotate
(C) jumping from a height
(D) tearing a paper into two pieces

Answer: D

Question. A body floats in water because:
(A) no force is acting on it
(B) the net force acting on this body is zero
(C) of gravitational pull
(D) friction between body and the water

Answer: B

Question. In which of the following activity, friction is useful?
(A) driving a car
(B) hitting a ball with bat
(C) rowing a boat
(D) sitting on a chair

Answer: D

Question. Which of the following is not a type of force?
(A) muscular
(B) magnetic
(C) chemical
(D) pulling a bucket of water from a well

Answer: C

Question. The atmospheric pressure is due to the:
(A) sky above our head
(B) air mass surrounding earth
(C) gravitational force of sun and other planets
(D) mass of the earth

Answer: B

Question. The pressure exerted by a liquid:
(A) increases with depth
(B) decreases with depth
(C) is constant
(D) first increases then decreases

Answer: A

Question. Which of the following statement is not true.
(A) A freely falling body is acted upon by gravitational force
(B) Pressure on top of mount everest is much more than 1 atm
(C) S.I. unit of pressure is pascal
(D) The blood vessels in our body maintains the internal pressure equal to the atmospheric pressure

Answer: B

Question. In which of the following cases the net force is not equal to zero?
(A) A kite skillfully held stationary in the sky
(B) A ball falling feeely from a height
(C) A helicopter hovering above the ground
(D) A cork floating on the surface of water

Answer: B

Question. Friction force is responsible changing:
(A) shape of an object
(B) direction of an object
(C) speed of an object
(D) all of the above

Answer: C

Question. Thrust is:
(A) Force X area
(B) Force / Area
(C) Pressure
(D) Pressure X Area

Answer: D

Question. A force of 16 N is distributed uniformly on one surface of a cube of edge '8' cm. The pressure on this surface is: 

(A) 3500pa
(B) 2500 pa
(C) 4500 pa
(D) 2000 pa

Answer: B

 

Q1. Define the following terms:

i) Force ii) Pressure iii) Streamline body

Q2. Name the following:

i) The force acting opposite to the kinetic friction.

ii) The instrument used to measure the pressure difference.

iii) Pressure exerted by the atmosphere.

iv) Force exerted by the earth.

Q3. Answer the following questions:

i) How is the gravitational force related to the mass of an object?

ii) Why can’t we use a beam balance to measure the weight of a body?

iii) Give two examples each of harmful friction and useful friction.

iv) How is the pressure in the liquids related to the depth?

v) How do the rockets sent to space do not fall back on the earth?

vi) What will be the weight of an object on Jupiter, whose weight is 1000 Kg on the earth?

vii) Why the cutting edge of a knife is made sharp?

1. Name the following: -

a. Force of attraction between any two bodies on earth.

b. Device used to measure weight of a body.

c. Bodies with the smooth outline.

d. Instrument used to measure pressure difference.

2. Differentiate the following: -

a. Static friction and Kinetic friction.

b. Magnetic force and Electrostatic force.

3. Draw diagram of the following: -

a. Spring Balance.

b. Manometer.

4. Give reasons for the following: -

a. Why the cutting edge of knife is made sharper?

b. Why is moon’s force of gravity less than that of Earth?

c. Why are Skis long and flat?

5. Very Short answer: -

a. Define Pressure.

b. SI unit of Pressure.

c. SI unit of Force.

1. Name the following: -
a. Force of attraction between any two bodies on earth.
b. Device used to measure weight of a body.
c. Bodies with the smooth outline.
d. Instrument used to measure pressure difference.

2. Differentiate the following: -
a. Static friction and Kinetic friction.
b. Magnetic force and Electrostatic force.

3. Draw diagram of the following: -
a. Spring Balance.
b. Manometer.

4. Give reasons for the following: -
a. Why the cutting edge of knife is made sharper?
b. Why is moon’s force of gravity less than that of Earth?
c. Why are Skis long and flat?

5. Very Short answer: -
a. Define Pressure.
b. SI unit of Pressure.
c. SI unit of Force.

Answer the following questions

1. Define the following terms:-

(a) Muscular force

(b) Gravitational force

(c) Electrostatic force

2. What is Resultant force? Expalin with the help of examples.

3. What are the effects of Force?

4. Differentiate between Magnetic Force and Gravitational Force.

5. Explain the significance of atmospheric pressure.

6. Complete the following table. Show the calculation stepwise in your science notebook.

7. Who was Blaise Pascal? Make a power point presentation on his findings.

1.The standard atmospheric pressure at sea level is -
(A) 10x10^-12N/m²
(B) 1x10²³ N/m²
(C) 10¹² N/m²
(D) 10⁵ N/m²

2.The effects of force are:
(A) Motion of an object
(B) Change in the magnitude of velocity of an object
(C) Change in direction of motion
(D) All of these

3.Which among the following are the types of forces-
(A) Magnetic force
(B) Nuclear force
(C) Gravitational force
(D) All of these

4.Friction forces act
(A) In the direction of force applied
(B) In the direction of the motion
(C) In the direction opposite to the direction of motion
(D) None of these

5.The effect of frictional force may be minimized by
(A) Using a smooth object
(B) Using a smooth plane
(C) Providing a lubricant at the surface of contact
(D) All of these

6.Negative value of force implies that
(A) Force is exerted on some other object
(B) Force is in the direction opposite to that of the motion
(C) Force is in the same direction to that of the motion
(D) Gravitational force is acting on the object

7.S.I. Unit of force is
(A) Newton
(B) Dyne
(C) Kg-wt
(D) Kg

8.Gravitational force acts between
(A) Sun and Planet
(B) Earth and Bodies
(C) All the bodies in the universe
(D) Sun and Earth

9.Which force can act from a large distance
(A) Magnetic
(B) electrostatic
(C) Gravitational
(D) All of these

10.A car slips on a wet road because
(A) Water increases the friction between the road and the tyres.
(B) It is not possible to apply brakes on a wet road
(C) The friction between the brakes shoes and the wheels is reduced
(D) Water reduce the friction between the road and the tyres

11.Friction force is
(A) Contact force
(B) Non-Contact force
(C) Muscular force
(D) None of these

12.Friction can be reduced by
(A) Polishing
(B) Oiling
(C) By use the ball bearing
(D) All of these

13.Two bodies in this universe attract each other by a force-
(A) Contact force
(B) Gravitational force
(C) Muscular force
(D) None of these

14.The weight of the body is because of
(A) Magnetic force
(B) Electrostatic force
(C) Gravitational force
(D) none of these

15.Any change in pressure on a confined gas produced a change in(A
) Volume
(B) Force
(C) Temperature
(D) All of these

16.A barometer is a compact device for measuring-
(A) Volume
(B) Height
(C) Pressure
(D) All of these

17.Atmospheric pressure at sea level support a column of mercury-
(A) 520 mm
(B) 25 mm
(C) 740 mm
(D) 760 mm

18.What happens when a body leaves the Earth's gravitational field?
(A) The body will no longer be pulled back to the earth.
(B) Speed of body decreases
(C) Body fall on the Earth.
(D) None of these.

19.Fill a glass with water and cover it with a coaster. Invert the glass. What happen?
(A) Water will spill
(B) Water will not spill
(C) Some water will spill and some will not
(D) None of these

20.The S.I. unit of pressure
(A) Pascal
(B) Newton
(C) Joule
(D) none of these

21.Gravitational force is a
(A) Contact force
(B) Consequential force
(C) Action at a distance force
(D) None of these

22.Friction is
(A) Always a disadvantage
(B) Always an advantage
(C) Sometimes a disadvantage and some times an advantage
(D) Neither an advantage nor a disadvantage

23.Rocket have a special streamline body in order to
(A) Increase friction
(B) Reduce friction
(C) Make them attractive
(D) none of these

24.Which force is contact force
(A) Gravitational

(B) Magnetic force
(C) Electrostatic force
(D) Frictional force

25.Grooves in tyres
(A) Increase friction of the tyre with the road.
(B) Decrease friction of the tyre with the road
(C) Do not affect friction of the tyre with the road.
(D) Make the tyre look good.

26.Burning of the meteor in the atmosphere is due to
(A) Electrostatic force
(B) Magnetic force
(C) Frictional force
(D) Gravitational force

27.A stone falling from the roof of a house is an example of
(A) Frictional Force
(B) Magnetic Force
(C) Gravitational Force
(D) Electrostatic Force

28.If area of a contact is increased, then
(A) Pressure increases
(B) Pressure decreases
(C) Pressure remain Constant
(D) none of these

29.Muscular force is an example of
(A) Contact force
(B) Non-Contact force
(C) Gravitational Force
(D) None of these

30.Pressure is directly proportional to the
(A) Area
(B) Force Applied
(C) a and b
(D) None of these

31.A charged comb attract small pieces of paper due to
(A) Frictional Force
(B) Magnetic Force
(C) Gravitational Force
(D) Electrostatic Force

32.What happen when two force act in opposite direction on an object?

33.What is a force?

34.Define the push force with its effect.

35.Define pull force and write its effects.

36.Explain the term contact force?

37.Define Muscular Force?

38.What is the Friction?

39.Explain the term Non-contact Forces?

40.What is the Magnetic Force?

41.What is the Electrostatic Force?

42.What happens when we press a rubber ball placed on a table?

43.How a force of friction arises?

44.Which device is used to measure the weight of a body?

45.Define the weight of a body. Also write its S.I. unit.

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46.What are the effect of force?

47.What is the Gravitational Force?

48.What is the Pressure?

49.What is the Atmospheric Pressure?

50.Define the term Gravity?

51.How does a person move forward during swimming?

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52.What happens when a force acts on an object? <

53.What do you mean by the force of friction? How can it be minimised?

54.Why does an empty can not cave in normally? <

55.Why is the moon's force of gravity less than that of the earth?

56.Mention three types of forces which can act from a distance.

57.fill the following situations Identify the agent exerting (he force ;<nrl the ot^ect on which it acts. State the effect of the force in each case.
(a) Squeezing a piece oflemon between the fingers tn extract its juice
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a nook fixed, to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.

58.A blacksmith hammers a hot piece of iron while making a loo!. How does the force due to hammering affect the piece of iron?

59.An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon slicks to the. wall. What force might be responsible for the attraction between the balloon and the wall?

60.Name the forces acting on a plastic bucket containing water held above, ground level in your hand. Discuss why the forces acting on the bi icket do not bring a change in its state of motion.

61.A nx&et has been fired upwards to launch a satellite in its orbit. Name two forces acting on the rocket immediately after leaving the launching

62.When we pxen the bulb of a dropper with its nozzle kept in water, air in (be dropper to)«it to escape in the form of bubbles. Once we release the jiscessure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to {£) pressure of water. gravity of the earth. shape of rubber bulb. *HW

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63.Mention three disadvantages of friction between the parts of a machine. How does (a) oiling and (b) using ball bearings help reduce friction?

64.Free-body diagrams for four situations are shown below. The net force is known for each situation. However, the magnitudes of a few of the individual forces are not known.

 

Q1 If a man stands on chair , chances of its breaking are more but if a man sits on chair, chances of its breaking are less. Explain.

Q2 Why do dams have broad base?

Q3 Show that liquid at a given depths exerts equal pressure in all directions.

Q4 Why does the nose of a mountaineer bleed at high altitudes?

Q5 Why does an astronaut wear a special type of suit?

Q6The pressure due to atmosphere is very large.Why are we not crushed?

Q7 In which case out of the following is it easier to lift the school bag full of books.

Explain a) school bag with thin and strong string.

b) school bag with a strip of wide cloth band

Q8. What makes a moving ball come to rest in a while even if no force is applied?

Q9. What makes a ball thrown up into the air fall back to the ground?

Q10. Why is the cutting edge of a knife made sharp?

Q11. What makes a coaster placed over the rim of a glass of water stick even when you invert it?

Q12. What is the characteristic that magnetic, electrostatic & gravitational forces have in common?

Q13. How is the pressure in a liquid related to the depth? How would you demonstrate this?

Q14. Calculate the pressure, if a force of 100 N acts on an area of 10 m² ?

Q15. Give reasons of the following:

a) Railway tracts are mounted on sleepers.

b) Camel can walk easily on sand.

c) Nails have pointed end.

d) Army tanks run over broad steel trail.

Q16. The tip of drawing pin has an area 1.0 x 10^-8 sq. m. Find the pressure exerted if force applied is 10 N?

Q17. A block of size 20 m x 10 m x 5 m exerts a force of 30 N. Calculate the maximum & minimum pressure exerted by block on ground?

I. Answer the following :

1. A push or pull on an object is called a ______________.

2. The state of motion of an object is described by its __________ and the direction of motion.

3. The force resulting due to the action of muscles is known as _____________ force.

4. Muscular force is also called as _____________ force.

5. The force exerted by a magnet and electrostatic force are examples of _____________ force.

6. Every object in the universe exerts a force on every other object called a _____________ force.

7. The force acting on a unit area of a surface is called _____________.

8. Pressure in liquids _____________ with the increase in depth of the liquid column.

 

II. Choose the correct answer:

1. Which of the following will exert the maximum pressure on ground while moving
a) an elephant
b) A girl wearing a pencil heel
c) Rhinoceros
d) Camel

2. Force can change
a) Only position of object
b) Only speed of object
c) Only direction of moving object
d) All the above

3. Which of the following is not a non-contact force
a) gravitational force
b) electrostatic force
c) muscular force
d) All of them

4. A force has
a) magnitude
b) direction
c) both of them
d) None of them

5. Which type of force is acting when hair is being pulled by a charged comb
a) Contact force
b) Non-contact force
c) both of them
d) None of them

 

CHAPTER 16 : LIGHT

I. Answer the following question :

1. Name the angle between the normal and the incident ray.

2. Name the angle between the normal and the reflected ray.

3. In an image formed by a mirror the left of the object appears on the right and vice-versa. This is known as _______________

4. Splitting of light into its colours is known as___________

5. Our eyes sees everything around us due to _________ light.

6. Name the small opening present in Iris.

7. Visually challenged persons can read and write using __________ system.

II. Choose the correct Answer :

1. When we say that a person has black, blue or green eyes, we refer actually to the colour of
a. Lens
b. Cornea
c. Iris
d. Pupil

2. The lens focuses light on the back of the eye, on a layer called
a. cornea
b. retina
c. lens
d. pupil

3. Among the following which cells are sensitive to bright light
a. rods
b. cones
c. Both
d. None

4. Among the following which cells are sensitive to dim light.
a. rods
b. cones
c. Both
d. None of them

5. An owl can see very well in night but not during the day because
a. It has more no. of cones and only a few rods
b. It has more no. of rods and only a few cones
c. Same no. of cones and rods