NCERT Solutions for Class 8 Science Chapter 11 Force are provided here with simple step-by-step explanations. These solutions for Force are extremely popular among class 8 students for Science Force Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of class 8 Science Chapter 11 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class 8 Science are prepared by experts and are 100% accurate.
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Question 1:
In the given figure , two boys A and B are shown applying force on a block. If the block moves towards the right, which one of the following statements 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:
There is unbalanced force on the block. The block will move in the direction of greater force. As the block moves towards right, it means that the magnitude of force applied by the boy A is more than that of boy B.
Hence, the correct answer is option (a).
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Question 2:
In the circuit shown in the given Figure, 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 (c) magnetic force alone
(b) electrostatic force alone (d) frictional force alone
Answer:
On passing the electric current through the coil, it produces magnetic field. This magnetic field cause the magnetic force on hammer and the hammer moves to strike the gong.
Hence, the correct answer is option (c).
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Question 3:
During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is
(a) force of gravity. (c) force of friction.
(b) electrostatic force. (d) magnetic force.
Answer:
During combing, similar charge is induced on hair edges. Due to which, electrostatic repulsion occur between similar charge on hair. So they are flying apart on combing.
Hence, the correct answer is option (b).
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Question 4:
in the given figure shows a container filled with water. Which of the following statements is correct about pressure of water?
(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
Answer:
Pressure increases with depth. So pressure at A < pressure at B < pressure at C.
Hence, the correct answer is option (d).
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Question 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:
Both magnetic and electrostatic forces are attractive as well as repulsive in nature.
Hence, the correct answer is option (d).
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Question 6:
Which one of the following forces is a contact force?
(a) force of gravity (c) magnetic force
(b) force of friction (d) electrostatic force
Answer:
Friction force acts only when surfaces of two objects are in contact.
Hence, the correct answer is option (b).
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Question 7:
A water tank has four taps fixed at points A, B, C, D as shown in the given figure . The water will flow out at the same pressure from taps at
(a) B and C (c) C and D
(b) A and B (d) A and C
Answer:
Pressure will be same at same height. Point B and C are at same height, so water will flow out at same pressure from taps at points B and C.
Hence, the correct answer is option (a).
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Question 8:
A brick is kept in three different ways on a table as shown in the given figure. The pressure exerted by the brick on the table will be
(a) maximum in position A (c) maximum in position C
(b) maximum in position B (d) equal in all cases.
Answer:
As, pressure = force / area on which it acts.
So, if same force is applied on smaller area results more pressure. As area in contact with the surface in position A is minimum, so the pressure exerted by the brick on the table is maximum in position A.
Hence, the correct answer is option (a).
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Question 9:
A ball of dough is rolled into a flat chapatti. Name the force exerted to change the shape of the dough.
Answer:
Force can cause the change in shape of an object. The muscular force exerted by hand on the dough can change the shape of it into chapatti.
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Question 10:
Where do we apply a force while walking?
Answer:
While walking, we apply a force on ground in backward direction and we apply it with the help of our foot to move forward.
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Question 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:
If a girl is applying force in east direction her friend should also apply the force in east direction because if two forces will be acted in same direction the net force will increase and hence the box moves faster in same direction.
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Question 12:
In the circuit shown in the given figure, when the key is closed, the compass needle placed in the match box deflects. Name the force which causes this deflection.
Answer:
On closing the key, electric current starts flowing through the coil. Due to which, magnetic field is produced and hence magnetic force starts acting on the needle of the compass. This magnetic force deflects the compass needle.
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Question 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 dry clothes made of synthetic fibre often acquire charges on them, hence they stick to skin due to electrostatic force.
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Question 14:
While sieving grains, small pieces fall down. Which force pulls them down?
Answer:
Earth attracts every body towards itself by gravitational force. While sieving, grains fall down because gravitational force or force of gravity by earth on grains.
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Question 15:
Does force of gravity act on dust particles?
Answer:
Yes, force of gravity acts on dust particle. Force of gravity acts on every massive objects towards the earth.
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Question 16:
A gas filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity?
Answer:
The balloon is moving upwards, therefore net force on balloon is upwards. This could be possible if the upward force is greater than gravitation force, hence the force acting in upward direction is larger than the force of gravity.
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Question 17:
Does the force of gravitation exist between two astronauts in space?
Answer:
Yes, Gravitation force exist between two astronauts in space. Any two objects that have mass, there will be gravitation force in between them.
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Question 18:
A chapati maker is a machine which converts balls of dough into chapati’s. What effect of force comes into play in this process?
Answer:
When the force is applied on dough ball, its shape get converted to a disc, hence the effect of force is change in shape of the dough.
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Question 19:
In the given figure shows a man with a parachute. Name the force which is responsible for his downward motion. Will he come down with the same speed without the parachute?
Answer:
Force of gravity or gravitational force of attraction by earth on the man is responsible for its downwards movement. The air drag on the parachute acting opposite to the force of gravity, slows down the speed of the man. So, if man jumps without the parachute, his speed will be more.
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Question 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 car is moving with the same speed, it means the net force on the car is zero, this could only be possible if two forces acting on the car are equal in magnitude and opposite in direction. Therefore, we infer that magnitudes of two forces are equal in magnitude and opposite in direction.
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Question 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:
The thermocol balls held close to each other might move away from each other due to electrostatic force. The balls have similar charges and thus they move away due to repulsion between similar charges.
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Question 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:
In the given case, the gravitational force arises due to interaction between the earth and fruit.
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Question 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:
In order to slow down the cart, man has to pull the cart up the slope.
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Question 24:
In the given figure shows a car sticking to an electromagnet. Name the forces acting on the car? Which one of them is larger?
Answer:
Car is sticking to an electromagnet, due to magnetic force of attraction by electromagnet. There are two main forces, magnetic force in upward direction and force of gravity in downward direction, acting on the car. In this situation, the magnetic force in upward direction is more than the force of gravity.
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Question 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 ultimately falls down.
Answer:
The archer stretches the string of the bow by applying muscular force. In the process the shape of the bow changes and when the string is released, it regains its original position that provides the initial force to set the arrow in motion. The arrow ultimately falls down because there is gravitational force exerting downward on the arrow downwards.
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Question 26:
It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
Answer:
The area of blunt blades is larger as compared to the area of sharp-edged blades.
Therefore, the applied force produces a lower pressure in case of blunt blades, due to which it is difficult to cut the cloth.
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Question 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 the given figure. Which one of them will sink more? Why?
Answer:
Pressure = Force/area,
Thus, the smaller the area, the more will be pressure for same force(weight of rod). Pressure due to the thinner rod (i.e. rod B) on the sand will be more and hence, it will sink more in the sand.
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Question 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:
While walking on the sandy beach, woman wearing sandals with flat soles will feel more comfortable. The flat soles have larger area as compared to the sandals with pointed heels. As two women are of the same weight, force applied by them on the ground is same. Therefore, the pressure exerted by the pointed heels will be more compared to that with sandals having flat soles. Thus, the pointed heel sandals will sink more in the sand than the flat sole sandals and hence walking with flat sole sandals will be more comfortable.
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Question 29:
It is much easier to burst an inflated balloon with a needle than by a finger. Explain.
Answer:
Smaller the area, the more will be pressure for same force. Surface area of needle is less than finger, so more pressure can be exerted on the balloon by needle than finger. Hence, it is much easier to burst an inflated balloon with a needle than by a finger.
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Question 30:
Observe the vessels A, B, C and D shown in the given figure carefully. 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:
Pressure at the base depends on density of liquid and the height of the liquid column in the container. As the liquids in all the container is same (same density) and height of liquid column in the containers are in the order D > B > A > C. So, the decreasing order of pressure at the base on the containers is D > B > A > C.
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