RBSE Solutions for Class 8 Science Chapter 11 Force and Pressure

Rajasthan Board RBSE Solutions for Class 8 Science Chapter 11 Force and Pressure Textbook Exercise Questions and Answers.

RBSE Class 8 Science Solutions Chapter 11 Force and Pressure

RBSE Class 8 Science Force and Pressure InText Questions and Answers

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Question 1. 
A magnet attracts a piece of iron towards it. Is attraction also a pull? What about repulsion between similar poles of two magnets? Is it a pull or a push?
Answer:
Yes, attraction is also a pull and repulsion between similar magnetic poles is a push.

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Question 2. 
Does it mean that the net force on an object is zero if the two forces acting on it in opposite directions are equal?
Answer:
Yes, in this situation the net force will be zero.

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Question 3. 
I have seen fountains of water coming out of the leaking joints or holes in pipes supplying water. Is it due to the pressure exerted by water on the walls of the pipes?
Answer:
Yes, it is due to the pressure exerted by water on the walls of the pipes.

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Question 4. 
If the area of my head were 15 cm x 15 cm, how much force air will event on my head?
Answer:
The force due to air in a column of the height of the atmosphere and area 15 cm x 15 cm is nearly equal to the force of gravity of an object of mass 225 kg (2250 N). The reason we are not crushed under this force of gravity is that the pressure inside our bodies is equal to the atmospheric pressure and balances the pressure from outside.

RBSE Class 8 Science Force and Pressure Textbook Questions and Answers     

Question 1. 
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer:
Examples of change of the state of motion of objects due to push:

• To bring a book in motion, which is lying on a table.
• To close the drawer of a table.

Examples of change of state of motion of objects due to pull:

• To pull a bucket of water out of the well.
• To open the drawer of a table.

Question 2. 
Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:

• When a cyclist sits on the saddle (seat) of a bi - cycle, the shape of the spring changes.
• The shape of a rubber ball changes when it is pressed.

Question 3. 
Fill in the blanks in the following statements:
(a) To draw water from a well we have to ...................... at the rope.
(b) A charged body ...................... an uncharged body towards it.
(e) To move a loaded trolley we have to ...................... it.
(d) The north pole of a magnet ...................... the north pole of another magnet.
Answer:
(a) pull 
(b) attracts 
(c) push 
(d) repels.

Question 4. 
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill in the gaps in the following statements using the following terms : muscular, contact, non -contact, gravity, friction, shape, attraction.
(a) To stretch the bow, the archer applies a force that causes a change in its ...................... .     
(b) The force applied by the archer to stretch the bow is an example of ...................... force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a ...................... force.
(d) While the arrow moves towards its target, the forces acting on it are due to ......................  and that due to ...................... of air.
Answer:
(a) shape 
(b) muscular 
(c) contact 
(d) gravity, friction.

Question 5. 
In the following situations identify the agent exerting the force and the object On which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to 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 hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
Answer:

Question 6. 
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer:
The piece of iron flattens due to the force of hammering.

Question 7. 
An inflated balloon was pressed against a wall after it had been rubbed with a piece of synthetic cloth. It was found that the balloon sticked to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer:
Electrostatic force.

Question 8. 
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Answer:
Forces acting on a plastic bucket filled with water are:

1. Gravitational force on water and plastic bucket (acting downward)
2. Muscular force hands (acting upwards). Both of the above forces are equal in magnitude and opposite in direction. Therefore they cancel each others effect.
3. The muscles get pulled due to the weight of bucket and water. Hence there is no change in the state of motion of the bucket. 

Question 9. 
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer:
The forces acting on the launched rocket are:

• Gravitation force on rocket due to earth (acting downward).
• Thrust due to exhaust of gases produced by burning of rocket fuel (acting upward).

Question 10. 
When we press the bulb of a dropper with its nozzle kept in water, air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
(a) pressure of water
(b) gravity of the earth
(c) shape of rubber bulb
(d) atmospheric pressure.
Answer:
(d) atmospheric pressure