REVISION QUESTIONS, CHAPTERS 1& 2, CLASS 9 PHYSICS

CLASS 9 Physics

Q1 Name any two basic quantities and write their SI units.

Q2.Name any two derived quantities and write their SI units.

Q3 What are the three requirements for selecting a unit of a physical quantity.?

Q4. Define “light year".

Q5. Compare the time periods of two pendulum of length 4m and 25 m.

Q6. State two factors affecting the time period of a pendulum. State the effects also.

Q7. Distinguish between speed and velocity.

Q8. A car is moving with a velocity of 20 m/s. The brakes are applied to retard it at a rate of 2m/s². What will be the speed after 5 s of applying the brakes?

Q9. What does the slope of following graphs represent?

i) displacement-time graph ii) velocity-time graph

Q10. Derive the relation: S=ut + ½at² ( any method).

Q11. A body moves from rest with a uniform acceleration and travels 270 m in 3 s. Find the velocity of the body at 10 s after the start.

Q12. Define: i) acceleration ii) acceleration due to gravity.

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UNIFORM CIRCULAR MOTION

In uniform circular motion, 1. Speed is constant. 2. Velocity is variable and acts along tangential direction at a point. 3. Centripetal Force and acceleration act along the radius towards the centre if the circular path. 4. Centrifugal force appears to act radially outwards. It is a virtual ,fictitious force, not a real force.

ECHO IN LIVING ROOM

Why is echo not heard in our living rooms? To hear echo, the minimum distance between the source and the reflector must be 17m. When this distance is more than 17m, the reflected sound can be distinguished from the original. As the length of our rooms is less than 17m, we don't hear echo.

CONDITIONS FOR TOTAL INTERNAL REFLECTION. CLASS 10

1. The light ray should travel from denser to rarer medium. 2. The angle of incidence in the denser medium should be greater than the critical angle for the given pair of media.

PHYSICS

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