# Force of friction distance ½ distance travelled ke

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= Force of friction × Distance ½\Distance travelled =K.E.Force of friction=K.E.Weight of vehicle1Therefore, the public bus will stop at a lesser distance. ½3.To bring the moving object to rest, the work done on the object should be equal to the kinetic energy of the moving objecti.e.,12mv2. 34.Kilowatt hour (kWh) is the largest practical unit of energy1 kWh = 3.6 × 106JTherefore, 1.8 × 107Joule = 5 kWh. 35.(i) Power 1watt or J/s. 1 watt is the power of an object which does work at the rate of 1 J per second. 1(ii)Power of an object may vary. Hence, average power is important in the case when the average power of the entire process within a given time is calculated. 1Average power = Total energy consumedTotal time1(iii)P = mgh/t=(45 × 10 × 45 × 0.15)/9 = 375 W 1[CBSE Marking Scheme, 2012]6. (i)K.E. = 12m × v2= 18.75 kJ = 18750 1v2= 18750215×1v = 2500m/s = 50 m/s 1(ii)E = Pt= 100 W × 4h = 0.4 kWh 1Energy consumed by it in a day = 0.4 × 3.6 × 106J 1= 1.44 × 106J[CBSE Marking Scheme, 2011]qqq
P-91S O L U T I O N SSOUNDCHAPTER14TOPIC-1Sound : Its Nature, Production, Propagation, Speed and ReflectionWORKSHEET-147Solutions1.When the speed of an object exceeds the speed of sound, it is said to travel in supersonic speed. For example, bullets, jet crafts etc., travel in supersonic speeds. 12.Longitudinal mechanical wave. 13. (i)The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of a wave. ½(ii) Speed of sound (v) = Wavelength (λ) × Frequency (υ) ½v =λυ(iii)Given, velocity, v= 339 ms–1Wavelength, λ= 1.5 cm =1.5100mWe know, Velocity = Wavelength × Frequency Therefore, Frequency =VelocityWavelength=3391.5100=339 ×100 1.5 Frequency = 22600 Hz 1[CBSE Marking Scheme, 2011]4.(a)The pitch of a sound depends on the frequency of vibration. The pitch of a sound is directly proportional to its frequency. 1 (b)(i)High Pitched SoundLow Pitched Sound1(ii)[CBSE Marking Scheme, 2011]5.Three features of transverse waves are :(i)The particles of the medium vibrates at right angles to the direction of propagation of wave.(ii)Transverse waves travels in the form of crests and troughs.(iii)They cannot travel through vacuum. 1 × 3 = 36.(a) Longitudinal wave. (b)Sound waves. 1(c)If T is the time period of the wave then, 1(i) after time interval T/2, the point will have a rarefaction ½(ii) after time T, the point will have a compres-sion. ½[CBSE Marking Scheme, 2011]7.(a)S. No.MusicNoise(i)Music produces a pleasing effect on our ears and mind.Noise is unpleasant.(ii)Frequency is high and produces regular waveform.Frequency is low and has irregular waveform.(iii)Musical sound shows no sudden changes of amplitude or wave-length.Noise shows sudden changes in amplitude and wavelength.3(b)Bats and Dolphins.Process :SONAR. 1 + 1 = 2
P-92S C I E N C E - IXWORKSHEET-148Solutions1.The vibration of the medium that travels along or parallel to the direction of the wave is called a longitudinal wave. In a sound wave, the particles of the medium vibrate in the direction parallel to the direction of the propagation of disturbance. Hence, a sound wave is called a longitudinal wave. 12.Quality or timbre. ½ + ½
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