**PHYSICS TESTPAPER**

**CLASS XI**

**GRAVITATION AND WAVES**

**Instructions**

*Questions 1 to 5 carries one mark each*

*Questions 5 to 10 carries 2 marks each*

*Questions 10 to 15 carries 3 marks each*

*Questions 16 and 17 carries 5 marks each*

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- What are mechanical waves?
- The time period of a vibrating source producing sound is 0.01 s. If the velocity of sound is 340 ms -1 calculate wave length
- State the principle of superposition of waves
- Why is gravitational potential energy negative?
- What is geosynchronous satellite?
- Derive a relation between wave velocity, frequency and wavelength
- What are transverse and longitudinal wave motions? Give an example for each type
- What is the effect of pressure on the speed of sound? Justify your answer.
- What is a progressive wave? Write an expression which represents a progressive wave.
- State the conditions necessary for a satellite to appear stationary.
- Define orbital velocity. Derive an expression for it.
- Define acceleration due to gravity. Show that the value of ‘g’ decreases with altitude or height
- State the laws of vibrations of stretched strings.
- Derive an expression for the escape velocity of a satellite projected from the surface of the earth.
- What is the maximum value of potential energy that can be possessed by a heavenly body? Give the general expression for potential energy of an object near the surface of earth
- State Kepler’s law of planetary motion. Deduce Newton’s law of gravitation from Kepler’s law.
- (a)What is Doppler Effect? (b) Derive an expression for the apparent frequency when a source moves towards a stationary observer. (c) A policeman on duty detects a drop of 15% in the pitch of the horn of a motor car as it crosses him. Calculate the speed of car, if the velocity of sound is 330 m/s

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