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Final Review PHY231 1 Sound and Waves freeway In the afternoon the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute Late at night the traffic flow is only 5 cars per minute What is the late night decibel level a 77 dB b 74 dB c 70 dB d 68 dB PHY231 2 Sound and Waves freeway In the afternoon the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute Late at night the traffic flow is only 5 cars per minute What is the late night decibel level a 77 dB The number of car per minute passes from 100 to 5 b 74 dB The intensity level has reduced by a factor 20 afternoon night 10 log 20 13dB c 70 dB night afternoon 13 80 13 67dB d 67 dB PHY231 3 Sound and Waves whistle A very loud train whistle has an acoustic power output of 100 W If the sound energy spreads out spherically what is the intensity level in dB at a distance of 100 meters from the train I0 10 12 W m2 a 78 3 dB b 81 6 dB c 89 0 dB d 95 0 dB PHY231 4 Sound and Waves whistle A very loud train whistle has an acoustic power output of 100 W If the sound energy spreads out spherically what is the intensity level in dB at a distance of 100 meters from the train I0 10 12 W m2 a 78 3 dB b 81 6 dB c 89 0 dBIntensity for spherical wave is given by d 95 0 dB Power P 100 I 0 000796 W m 2 4 R 2 4 3 14 100 2 I 0 000796 10log PHY231 10log 89 dB 12 10 I0 Area 5 Sound and Waves whistle A bat flying at 5 00 m s toward a wall emits a chirp at 50 0 kHz If the wall reflects this sound pulse what is the frequency of the echo received by the bat vsound 340 m s a 51 5 kHz b 51 2 kHz c 40 8 kHz d 50 5 kHz PHY231 6 A bat flying at 5 00 m s toward a wall emits a chirp at 50 0 kHz If the wall reflects this sound pulse what is the frequency of the echo received by the bat vsound 340 m s a 51 5 kHz b 51 2 kHz c 40 8 kHz bat is flying when emitting the chirp so d 50 5 The kHz v 340 femitted fs 50 7 kHz fs v v s 340 335 Chirp reflects with frequency of50 7 kHz The bat is then an observer flying toward the relflected wave v v 0 340 5 fo femitted 50 7 PHY231 51 5 kHz 7 v 340 Sound and Waves whistle A 500 Hz whistle is moved toward a listener at a speed of 10 0 m s At the same time the listener moves at a speed of 20 0 m s in a direction away from the whistle What is the apparent frequency heard by the listener The speed of sound is 340 m s a 473 Hz b 485 Hz c 533 Hz d 547 Hz PHY231 8 Sound and Waves whistle A 500 Hz whistle is moved toward a listener at a speed of 10 0 m s At the same time the listener moves at a speed of 20 0 m s in a direction away from the whistle What is the apparent frequency heard by the listener The speed of sound is 340 m s a 473 Hz The general doppler effect formula is b 485 Hz v v 0 f0 fs c 533 Hz v vs d 547 Hz since the oberver is moving away from the source v 0 0 since the source is moving toward the observer v s 0 v v 0 340 20 f0 fs fs 485 Hz PHY231 9 v v s 340 10 Oscillations spring A m 0 20 kg block rests on a frictionless level surface and is attached to a horizontal spring with k 40 N m The block is initially displaced 4 0 cm from the equilibrium point and then released A frictional force of 0 3 N exists between the block and surface What is the speed of the block when it passes through the equilibrium point after being released a 0 45 m s b 0 63 m s c 0 80 m s d 1 2 m s PHY231 10 The mass is initially displaced by A 0 04 m Oscillations spring The system loses energy through friction The work done by the friction force is Wfriction F friction A 0 3 0 04 0 012 J The kinetic energy is given by 1 KE SPE Wfriction kA 2 Wfriction 0 5 40 0 04 2 0 012 0 02 J 2 1 But KE mv 2 so 2 2m 2 0 2 v 0 45 m s a 0 45 m s KE 0 02 b 0 63 m s c 0 80 m s d 1 2 m s PHY231 11 Oscillations engine The motion of a piston in an automobile engine is nearly simple harmonic If the 1 kg piston travels back and forth over a total distance of 10 0 cm what is its maximum speed when the engine is running at 3 000 rpm a 31 4 m s b 15 7 m s c 7 85 m s d 3 93 m s PHY231 12 The motion of a piston in an automobile engine is nearly simple harmonic If the 1 kg piston travels back and forth over a total distance of 10 0 cm what is its maximum speed when the engine is running at 3 000 rpm a 31 4 m s b 15 7 m s c 7 85 m s d 3 93 m s The engine rotates at 3000rpm This means it does 3000 60 50 cycles per seconds Thus the pistons runs at f 50 Hz The maximum speed is v A 2 f A 2 3 14 50 PHY231 0 010 15 7 m 13 s 2 Oscillations pendulum A simple pendulum has a mass of 0 25 kg and a length of 1 0 m It is displaced through an angle of 30 and then released After a time the maximum angle of swing is only 10 How much energy has been lost to friction a 0 29 J b 0 65 J c 0 80 J d 1 0 J PHY231 14 Oscillations pendulum A simple pendulum has a mass of 0 25 kg and a length of 1 0 m It is displaced through an angle of 30 and then released After a time the maximum angle of swing is only 10 How much energy has been lost to friction At the maximum angle of the swing all the energy is in gravitational potential energy GPE form a 0 29 J The difference in …
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