CBSE ADDA

CBSE Physics help class 8 Chapter: Sound 1. What is the difference between noise and music? Answer:     Unpleasant sounds are called noise whereas music is a sound, which produces pleasant sensation. But, if the musical sound is too loud, it becomes noise. 2. What is eardrum? How does it play an important role in hearing? Answer:     A thin tightly stretched membrane t is called eardrum. it vibrates sound wave and sends vibrations to the inner ear. 3.  Which property of vibrations determines the pitch of the sound? Explain giving some examples. Answer:     The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher the sound has a higher pitch. If the frequency of vibration is lower, the sound has a lower pitch. Women sound is shriller than man due to high frequencies 4. What is the audible range of frequencies for human beings? Answer:     The range of audible frequencies is roughly between 20 to 20,000

Q.1. Can any object have mechanical energy even if its momentum is zero? Explain. Yes, mechanical energy comprises of both potential energy and kinetic energy. Zero momentum means that velocity is zero. Hence, there it no kinetic energy but the object may possess potential energy. Q.2. The potential energy of a body is 39600J. How high is the body if its mass is 20kg? The potential energy of a body = mgh h = PE/mg = 39600j/20kg x9.8m/s 2 =198m Q.3. A force of 20 N displaces a body through a distance of 1 m at an angle of 60° from its own direction. Calculate the amount of work done. Here, force F = 20 N, displacement, s = 1 m. Angle between force and displacement 60°. Work done,W =Fscos0 =20 X 1 X cos60°=20X 1 X 1/2 = 10J. A man of 50 kg jumps up to a height of 1.2 m. What is his potential energy at the highest point? The potential energy of man = mgh = = 50 + 10 X 1.2 J = 600 J Q.4. How much work is done by a force of 10 N in moving an object through a distance o

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     Measurement and Motion   :Quest Time 1. Name one object that shows multiple motions? Ans: The Earth - Rotatory and translator motion Drilling - Rotatory and downward translator motion A ball moving along the ground- Rotatory and Rectilinear motion      2. How will you measure length in SI system? Ans: Using meter scale 3. What is the quantity that can be measured? Ans: Physical quantity like mass, length and Time 4. What type of motion body moves as a whole? Ans: Translatory motion 5.Which kind of motion produce sound? Ans: Vibratory motion 6. What types of motion is noticed in the pendulum of clock and swing? Ans: Oscillatory motion and periodic 7.  Falling of apple from tree is what types of motion? Ans: Rectilinear motion. 8. Discovery of what made transport easy? Ans: Wheel 9. Motion in which the distance from the axis remain same? Ans: Circular motion 10. To and fro motion of a body about a fix point is example of