We have Provided the CBSE Solutions chapter-wise. Class 8 Science Chapter 11 Force and Pressure with Answers by expert subject teacher for latest syllabus and examination. Students can take a free CBSE Solutions of Force and Pressure. Each question has right answer Solved by Expert Teacher.
CBSE Solutions Class 8 Science Beehive Prose
Page No. 142
Q1. Give two examples each of situations in which you push or pull to change the state of motion of objects.
Answer: Two examples of push force are as follows:
- A heavy box at rest is pushed to move it from one room to another. This changes the state of motion of the box.
- A player pushes a football using his foot. This changes the state of motion of the ball.
Two examples of pull force are as follows:
- Rope is pulled to draw water from a well. This changes the state of motion of the water bucket.
- A drawer is pulled to open it. This changes the state of motion of the drawer.
Q2. Give two examples of situations in which applied force causes a change in the shape of an object.
Answer: The forces which change the shape of an object are as follows:
i) By pressing the clay between the hands, it deforms.
ii) The shape of the plastic bottle changes by squeezing it.
Q3. 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.
(c) 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
Q4. 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 .
(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
(d) gravity and that due to friction of air.
Q5. 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: (a) Agents are fingers, object is lemon, effect of force changes the shape of lemon.
(b) Agents are fingers of the person squeezing the tube, object is toothpaste tube and effect of the force can be observed as the paste coming out of the tube (change in shape).
(c) Agent is the load suspended, object is the spring and effort can be seen in the form of elongation of spring on suspension of load (change in shape).
(d) Agent is muscles of athlete, object is athlete himself and effect of the force changes the state of motion of the athlete.
Q6. 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 shape of the hot piece of iron changes. It flattens and becomes thinner than earlier. This is the effect of force due to hammering the piece of iron.
Q7. 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?
Answer: On rubbing an inflated balloon with a piece of synthetic cloth, it becomes charged. A charged body attracts an uncharged body. When this charged balloon is pressed against a wall, it sticks to the wall. The force acting between the charged balloon and the wall is the electrostatic force.
Q8. 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: The bucket is help up by the action of muscles in our body in the upward direction and force of gravity acting downwards. The force resulting due to the action of muscles in our body is known as muscular force.
Thus, the bucket is held in position by the action of upward and downward force.
The forces do not bring the change in its state of motion because they are acting in opposite direction with equal magnitude. Hence, bucket stays in the same position.
Q9. 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 two forces acting on the rocket immediately after leaving the launching pad are:
- Upward force applied by the rocket engine.
= Downward gravitational force applied by the earth.
(Ignoring frictional force due to air resistance)
The upward force due to rocket engine exceeds the downward gravitational force which makes the rocket move upward.
Q10. 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
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