NCERT Exemplar Solution Class 8 Science Chapter 11
NCERT Exemplar Solution Class 8 Science Chapter 11 Force all Questions Answer Solution. NCERT Exemplar Class 8 Science Chapter 11 Solution PDF.
NCERT Exemplar Solution Class 8 Science Chapter 11: Overview
NCERT Exemplar Solution Class 8 Science Chapter 11 |
|
Board |
NCERT |
Topic |
Exemplar Problem Solution |
Class |
8 |
Subject |
Science |
Chapter |
11 |
Chapter Name |
Force |
NCERT Exemplar Solution Class 8 Science Chapter 11 Force
Multiple Choice Questions
1)
A B
Fig. 11.1
In fig. 11.1 , two boys A and B are shown applying force on a block. If the block moves towards the right, which one of the following statement is correct?
a) Magnitude of force applied by A is greater than that of B.
b) Magnitude of force applied by A is smaller than that of B.
c) Net force on the block is towards A.
d) Magnitude of force applied by A is equal to that of B.
Answer:- a) magnitude of force applied by A is greater than that of B.
If the block is moved towards the right side then force applied by the A will be greater than B.
2)
Fig. 11.2
In the circuit shown in fig. 11.2 when the circuit is completed, the hammer strikes the gong. Which of the following force is responsible for the movement of hammer?
a) Gravitational force alone
b) Electrostatic force alone
c) Magnetic force alone
d) Frictional force alone
Answer:- c) Magnitude force alone
The magnitude of force is responsible for the movement of hammer. As soon as the circuit complete the hammer sticks with the force on gong and thus the bell rings.
3) During day weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is
a) Force of gravity
b) Electrostatic force
c) Force of friction
d) Magnetic force
Answer:- b) Force of Friction
Force of friction takes place while we comb hair in the dry weather. There is some charge takes place over there.
4) Fig. 11.3 shows a container filled with water. Which of the following statements is correct about pressure of water ?
Fig. 11.3
a) Pressure at A> pressure at B> pressure at C
b) Pressure at A = pressure at B = pressure at C
c) Pressure at A< pressure at B > pressure at C
d) Pressure at A < pressure at B < pressure at C
Answer:- d) pressure at A < Pressure at B < pressure at C.
The maximum pressure of water is exerted below on the surface thus pressure exerted on the C is greater than B than A.
5) Two objects repel each other, this repulsion could be due to
a) Frictional force only
b) Electrostatic force only
c) Magnetic force only
d) Either a magnetic or an electrostatic force
Answer:- d) Either a magnetic or an electrostatic force.
Repulsion can be occur between two magnetic bodiesdue to magnetic force and in other bodies electrostatic force of repulsion occurs.
6) Which one of the following forces is a contact force?
a) Force of gravity
b) Force of friction
c) Magnetic force
d) Electrostatic force
Answer:- b) Force of Friction
Friction takes place due to contact Between two objects thus it is a contact force. Muscular force is also an contact force. All the other are non – contact forces.
7)
Fig. 11.4
A Water tank has four taps fixed at points A, B, C, D as shown in fig. 11.4 the water will flow out at the same pressure from taps at
a) B and C
b) A and B
c) C and D
d) A and C
Answer:- a) B and C
B and C both the taps are fixed on the same position therefore the water will exert with the same pressure.
8)
A B C
A brick is kept in three different ways on a table as shown in fig. 11.5 the pressure exerted by the brick on the table will be
a) Maximum in position A
b) Maximum in position B
c) Maximum in position C
d) Equal in all cases.
Answer:- a) Maximum in position A.
Smaller the area greater is the force exerted by it therefore Brick in position A will exert more pressure on the ground.
very Short Answer Questions
9) A ball of dough is rolled into a flat chapatti. Name the force exerted to change the shape of the dough.
Answer:- Muscular force is extended on the dough to change the shape and rolled into a flat chapatti.
10) Where do we apply a force while walking?
Answer:- we apply force on the ground while walking.
11) A girl is pushing a box towards east direction. In which direction should her friend push the box so that it moves faster in the same direction?
Answer:- her friend should push the box into the same direction that is east direction so that the box should move faster.
12) In the circuit shown in fig. 11.6 when the compass needle placed in the match box deflects. Name the force which causes this deflection.
Fig. 11.6
Answer:- The compass needle placed in the match box deflects due to the magnetic force When the current is passed through the circuit.
13) During dry weather, clothes made of synthetic fibre often stick to the skin, which type of force is responsible for this phenomenon?
Answer:- The electrostatic force of attraction is responsible for the phenomenon that clothes made of synthetic fibre often stick to the skin in dry weather.
14) While sieving grains, small pieces fall down. Which force pulls them down?
Answer:- sieving is an method of separating grains, during these small pieces fall down. The force which is responsible to these action is gravitational force of attraction. I.e force of gravity which attracts the grains towards it.
15) Does force of gravity act on dust particles?
Answer:- yes. Force of gravity also acts on the dust particles. Although dust particles scattered in the air and moving freely. But gravitational force attract these dust particles and it settled down on the ground.
16) A gas filled balloon moves up. Is the upward force acting on it. Larger or smaller than the force of gravity ?
Answer:- yes. A balloon filled with gas moves up due to upward force acting on it. But it does not affect by the gravitational force because upward force is greater than the gravitational force acting on it.
17) Does the force of gravitation exist between two astronauts in space?
Answer:-. Yes. The force of gravitation exist between two astronauts in space. Gravity is not only on the earth alone. Every object small and large is exerted by the gravitational force in the whole universe.
Short Answer Questions
18) A chapati maker is a machine which converts balls of Dough into chapattis. What effect of force comes into play in this process ?
Answer:- The force exerted of chapati maker machine on the balls of Dough turns it into chapattis. And these changes the shape of the dough.
19) Fig. 11.7 shows a man with a parachute. Name the force which is responsible for this downward motion. Will he come down with the same speed without the parachute?
Fig. 11.7
Answer:- as shown in fig. 11.7. a man with parachute. The force which is responsible for the downward motion is gravitational force. But if he would come without parachute downwards he would not come with the same speed. He will come with the higher speed without parachute.
20) Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied.
Answer:- The forces acting on the moving cart are with equal magnitudes. And the direction of the forces applied are in opposite directions.
21) Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.
Answer:-
Both the Thermocol balls have an electrostatic force of attraction between them. Due to same charges on their body they repel each other and move away from each other.
22) Fruits detached from a tree fall down due to force of gravity. We know that a force arises due to interaction between two objects. Name the objects interacting in this case.
Answer:-. Fruits fall down due to gravitational force on the earth. Therefore theseforce arises between the two objects are earth and fruits.
23) A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he wants to slow it down. What should he do?
Answer:-. While pushing the cart down the slope,cart moves faster due to slope.but if he will pull the cart by applying force on the opposite direction then the cart will be slow down.
24) Fig. 11. 8 shows a car sticking to an electromagnet. Name the forces acting on the car? Which one them is larger ?
Fig. 11.8
Answer:- there are two forces acting on the car when it is stuck to the electromagnet. One is magnetic Force due to electromagnet acting in upward direction and another is gravitational force of earth acting downwards. Also the weight of car is responsible for the downward force. The larger force between the two forces is the magnetic force of an electromagnet.
Long Answer Questions
25) An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow intimately falls down.
Answer:-
The initial force acting on the bow by the Archer is the muscular force. By applying muscular force on the string is stretched and then release rapidly. After release the string gets its original position. And the arrow which is released in the air is finally falls down due to force of gravity acted on it.
26) It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
Answer:- pressure is the force per unit area.The smaller is the area the higher is the pressure acted upon the object. As the blunt blades of scissors have large area as compared to sharp edged blades of scissors. Thus the force which is applied on the blunt scissors produces lower pressure on cloth. While the blades with sharp edges produces higher pressure which makes easier in cutting the cloth.
27) Two rods of the same weight and equal length have different thickness. They are held vertically on the surface of sand as shown in fig. 11.9 which one of them will sink move? Why?
Fig. 11.9
Answer:-
The pressure is the force per unit area. Smaller the area higher the pressure exerted and Larger the area smaller the pressure exerted on the surface. Now, according to the figure, Rod A having larger area will produce less pressure on the surface and therefore it will not move or sink. But Rod B which is having the same weight but smaller area will produce higher pressure and thus it will move sink into sand.
28) Two women are of the same weight. One wears sandals with pointed heels while the other wears Sandals with flat soles. Which one would feel more comfortable while walking on a sandy beach? Give reasons for your answer.
Answer:-
Pressure exerted by the small area is larger than the pressure exerted by the large area. The two women having same weight will exert same pressure on the ground, Therefore pointed heals will exert more pressure on the sand as compared to the flat heels. And high pointed heels will sink more in the sand as compared to flat sandals. Therefore the woman wearing flat soles sandals will feel more comfortable.
29) It is much easier to burst an inflated balloon with a needle than by a finger. Explain.
Answer:-
Needle has an sharp pointed edge these small area exerts greater pressure on the inflated balloon, as compared to the finger. Therefore on pricking needle balloon gets burst easily.
30) Observe the vessels A, B, C, and D shown in fig. 11.10 carefully.
A B C D
Fig. 11.10
Volume of water taken in each vessel is as shown. Arrange them in the order of decreasing pressure at the base of each vessel. Explain.
Answer:-
The pressure of liquid depends upon the volume of the liquid and not upon the height of the containers, therefore the decreasing order of the pressure exerted on the base of each vessels will be B, D, A, C.