CBSE ADDA

1.A submarine enters a sonar pulse, which returns from an under water cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff? Ans: t = 1.02s, v = 1531m/s Now d=s x t Distance travelled by sonar pulse = 2d = 2x1531x1.02 = 1561.62m Distance of the cliff = d/2= 1561.62/2 = 780.81m 2. If the tension in the wire is increased four times how will the velocity of wave in a string varies? Answer: velocity of the wave in string is directly proportional to the square root of the tension thus if tension is increased 4 times the velocity will be doubled. 3. What is Echo. Explain the conditions that have to be satisfied to hear an echo? Ans: reflection of sound wave from a large obstacle is called an echo. The most important condition for hearing an echo is that the reflected sound should reach the ear only after a lapse of at least 0.1 second after the original sound dies off and the obstacle is at least at a distance of 17 m 4. Why do echoes produced in an

Fully Solved Questions from previous year board Paper Question: 1. What causes buoyant force (or up thrust) on a boat? Answer: Buoyant force is due to volume of boat and density of water. Question: 2. what is the cause of buoyant force? Answer: : The pressure difference on lower part and upper part of a body cause of buoyant force . Question: 3. An Object of volume V is immersed in a liquid of density P. Calculate the magnitude of buoyant force acting on the object due to the liquid Answer: Vd g Question: 4. why does a block of wood held under water rise to the surface when released? Answer: This happens because as upward force is greater than the weight. Question: 5. What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid. When does the buoyant force become maximum? Answer: The buoyant force exerted by a fluid is equal to the weight of fluid displaced. Therefore the buoyant force increases as more and more vol

IX Class Question solution for Physics Chapter Sound 1. How sound is produced? Answer:   Sound is produced by the vibration of vibrating object. 2. What do you understand by a ‘wave’? Answer:  A periodic disturbance created in material medium that transfer sound and light energy is called wave. 3. Write three differences between sound and light waves. Answer:   sound wave is Mechanical wave that require material medium for propagation where as light waves are electromagnetic wave that can travel in vacuum. 4. What do you understand by “sound energy cannot be produced”? Answer: Sound energy cannot be produced on its own. Some mechanical energy is required to make an object vibrate. It is the mechanical energy of the vibrating object which travels through a medium and ultimately reaches the ear. 5. What is the name of the wave that can travel through vacuum? Answer:   Electromagnetic wave 6. Explain by some experiment that sound waves require medium for their

1 Mark Questions Q1. Which sound has a higher pitch, guitar or car horn? Q2. Name three animals which can hear ultrasonic vibrations. Q3. How are the wavelength and frequency of a sound related to its speed? Q4. Why sound wave is called a longitudinal wave? Q5. Frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute? Q6. What is an echo? Q7.What do waves transport - matter or energy? Q8. What is a wave? Q9. Which characteristics of the sound help us to identify a person by his voice if he is sitting in a dark room? Q10. If the amplitude of a wave is doubled, what will be the effect on its loudness? 2 Marks Questions Q11. Which wave property determines a) loudness, b) Pitch? Q12. Why are the ceilings of concert halls curved? Q13. How is ultrasound used for cleaning? Q14. Sound is produced due to a vibratory motion, then why a vibrating pendulum does not produce sound? Q15. A sound produces 20 crests and 20 troughs in 0.4 sec. Find the frequenc

Two marks questions  1. Explain how echoes are used by bats to judge the distance of an obstacle? 2. State the special properties of ultrasound that make it useful to us .In general, how these properties are utilized. 3. Why is soft furnishing avoided in concert halls? 4. Draw a diagram depicting low pitched sound and high pitched sound and write main difference between the two? 5. Distinguish between longitudinal and transverse waves. Give one example each. 6. An explosion takes place at the moon. After what time would it be heard at the earth? Three marks questions 7. Two sources A and B vibrate with the same amplitude. They produce sounds of frequencies 1 kHz and 30 kHz respectively. Which of the two waves will have greater power? 8. Find the time period of the source of a sound wave whose frequency is 400Hz. 9. A sound wave travels at a speed of 340m/s. If its wavelength is 2 cm, what is the frequency of the wave? Will it be in the audible range? 10.

Q. If you want to lift the water to damp against the force of gravity what is the energy used by motor.given that Mass=20Kg ; Height=20m;Gravity=9.8m/s; Time=20min Ans: Work done by the motor against the gravity, W = mgh = 20×9.8×20 = 3920 J Power delivered by the motor = W/t =3920/(20×60) = 3.27 J/s Q. when a ball is lifted to a height of height h when it is drooped just before touching the ground, what would the kinetic energy acting on the ball. Ans: mgh According to the conservation of energy Potential energy is converted into kinetic energy just above the ground. Just before touching the ground the kinetic energy of the body is equal to mgh Q. what are the conditions where the work can be zero? Ans: Work done is said to be zero if the force is acting at right angles to the displacement of the body or when there is no displacement of the body. Example: Work done by the force of gravity on box lying on a roof of a bus moving with a constant velocity on a straight