NCERT solution for class 8 // Science // Chapter 11 -Force and pressure

 NCERT solution > Class 8 > Science

  Chapter 11 - Force and pressure 

Exercise 

Q1. Give two examples of each of situation in which you push or pull to change the state of motion of objects? 

Answer- Push - Shut the door by pushing 

And Close drawer by pushing 

Pull - Open drawer by Pulling 

Bullock pulls a bullock cart

Q2. Give two examples of situations in which applied force causes a change in the shape of an object? 

Answer- 1) When we prepare chapati from dough 2) when we make statue from clay

Q3. Fill in the blanks in the following statements 

a) To draw water from a well we have to pull at the rope .

b) Exchange the body attracts an unchanged body towards it .

c) To move a loaded trolley we have to push it.

d) The north pole of a magnet repels and the north pole of the another magnet 

Q4. Archer stretches her bow while taking aim at the target she then release the arrow which begin to move towards the target based on this information fill ups the gaps in the following statement 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 bows 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 situation identify the agent exerting the force and the object on which IT act state the effect of the force in each case .

a) Screening a piece of lemon between the fingers to exert it's 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 its shape of lemon .

b) agents are finger ,Object is toothpaste tube ,Effect of change paste squeezing out 

c) Agent is the load suspended object is the spring and if that can be seen in the form of elongation of spring 

d) Agent is muscles of athlete object is athlete and effect of the force changes the state of motion of athlete

Q6. A blacksmith hammers hot piece of iron while making a tool how does the force due to hammering affect the piece of iron .

Answer-  The force due to hammering it causes the change in the shape of the iron and iron can be molded in the shape of particular tool

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- Electrostatic force

Q8. Name the forces acting on a plastic bucket containing water held above ground level in your hand discuss why the force acting on the bucket do not bring a change in its state of motion? 

Answer- Force acting on a bucket are muscular force and force of gravity 

Both the forces do not change in the state of the motion because both are applying in opposite direction in equal form so they cancel the each other effect

Q9. A rocket it has been fired upward to launch a satellite in its orbit name the two forces acting on the rocket immediately after leaving the launching pad .? 

Answer- The forces that act on the rocket why launching pad are gravitational force of the Earth which is applied downward while frictional force of air in in opposite direction that is backward

Q10. When we Praise the bulb of a dropper with its nozzle and kept in water air in the dropper is seen to escape in the form of bubble once we release the pressure on the bulb water gets filled in the drop of the rise of water in the dropper is due to

a) Pressure of water 

b) Gravity of the earth  

c) Shape of the rubber bulb  

d) Atmospheric pressure 

Answer- Atmospheric pressure.


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