NCERT Class 8 Science Chapter 11 Solution
Brief Information: This post contains the solution for Chapter 11 Force and Pressure of Class 8 of the CBSE and also Gujarat Board (GSEB) books by GCERT (based on new NCERT).
Q1. Give two examples each of the situations in which you push or pull to change the state of motion of objects.
Push: We push the car the change its state of motion.
We push refrigerator door to close it.
Pull: The cart is pulled by the beast of burden.
We pull drawer out to open it.
Q.2 Give two examples of situations in which applied force causes a change in the shape of an object.
Ans. 1. Application of force by hammer on the iron piece changes its shape.
2. Squeezing of fruit like lemon, orange, melon etc changes its shape.
3. Change in shape of dump by pressing it downward by the hands.
4. Change in shape of spring when pulled from both the ends.
Q.3.Fill in the blanks in the following statements.
(a) To draw water from a well we have to pull at the rope.
(b) A charged body attracts an uncharged body towards it.
(c) To move a loaded trolley we have to push it.
(d) The north pole of a magnet repels the north pole of another magnet.
Q.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 up 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 shape.
(b) The force applied by the archer to stretch the bow is an example of muscular force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.
(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air.
Q.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.
Ans. Agent exerting force – Fingers
Object on which force acts – Lemon
Effect of force – Change in the shape of lemon. Lemon juice comes out of the lemon.
(b) Taking out paste from a toothpaste tube.
Ans. Agent exerting force – Fingers of a person squeezing the toothpaste tube.
Object on which force acts – Paste
Effect of force – Change in the shape of toothpaste tube. As a result paste comes out of the tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
Ans. Agent exerting force – Load suspended
Object on which force acts – Spring
Effect of force – Change in the shape of Spring. The spring Stretches.
(d) An athlete making a high jump to clear the bar at a certain height.
Ans. Agent exerting force – Legs of the athlete
Object on which force acts – Athlete himself
Effect of force – The force changes the motion of the athlete.
Q.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?
Ans. Iron is a malleable metal. The shape of iron piece changes when a blacksmith hammers a hot piece of iron. It can be moulded in the shape of required tool.
Q.7. 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 sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Ans. Electrostatic force is responsible for the attraction between the balloon and the wall.
Q.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.
Ans. When a bucket is held in hand following forces act upon it:
A.) Gravitational force of earth acting downward.
B.) Muscular force of hand acting upward.
The forces acting on bucket do not bring change in the state of motion as both the forces are acting in equal but opposite direction.
Q.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.
Ans. Immediately after leaving the launching pad following forces act on the rocket:
1. Gravitational force of the earth – downward towards the earth
2. Frictional force of air– in opposite direction to movement of the rocket
Q.10. Answer the following quetion.
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
(d) Atmospheric pressure