Class 8 Physics Important questions and answer

Attempts all the questions

1. Define measurement?

2. Define Motion and rest? Why rest and motion are interrelated?

3.Prove this:     

a.V=u +  at

b.S=S=(u+v)/2

  

4.Differences Between:          

a.Rest and motion

b.Motion and velocity

c.Scalar and vector
d.local action and polarization.
e.wave length and wave frequency

5.Numerical Problems:

a. A box has 300 kg mass. The surface area of the box is 150 m². What is the pressure exerted by the box on the floor:

b.A load of 500 kg is lifted up using a first class lever. Different effort distances and their corresponding efforts are shown in the table below. How far is the load from the fulcrum? Also find the values of A, B, C, and D.

ED	10 cm	A	c	40cm	100cm
Effort	100N	500N	200N	B	D

c.A car starts to move from the rest position. If the final velocity of the car is 20 m/s after 10 seconds, calculate the acceleration of the car.

       6. What is a simple machine? Give examples of each first and second class of lever.

7. Define 1 solar day and 1 meter.

8. What is one joule work? Write the type of work.

9. What it the transformation of energy and refraction of light?

       10. What is an echo? What does the frequency of sound if 70 Hz mean?

11. Write the molecular theory of magnetism. Write any two defects of a simple  machine

12. What is a frictional force and what is the advantage of it?
13. What are heat and sound?

14. Give reasons:

1. A sharp knife cuts more easily than blunt one, why?
2. An efficiency of the car is 80 %, why?
3. A lever has its MA 4, why?
4. Eggs sink in fresh water but float on salt water. Justify?
5. An electric bulb is marked 60W. What does it mean?
6. Why is water not used in thermometer?
7. Why is an alcohol thermometer not used to measure B.P of water?
8. Why do we refer to convex mirror as a rear view mirror in vehicles?
9. How are radii of curvature and focal length of a spherical mirror related?
10. The sound is a mechanical wave, why?
11. The sound is repeated near hills, why?

15. Some Difficult questions?

1. Why does a magnet get demagnetized when hammered?
2. Describe house wiring system in short?
3. Why does the stick, immersed into water, look bent? Explain with a ray diagram.
4. A man pushes a spear onto the fish which he sees inside the water. Do you think that the spear will hit the fish? Give answer with reasons.
5. What is the reverberation for echo? What are the conditions for reverberation to occur?
6. A magnet has more magnetic force at poles and less in the middle. Why?
7. Describe the structure of a dry cell in short.
8. What is a fuse? How does it work as a safeguard?

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