ConcepTest 11.1a ConcepTest 11.1a Harmonic Motion I 1) 0 2) A/2 3) A 4) 2A 5) 4A A mass on a spring in SHM has amplitude A and period T. What is the total distance traveled by the mass after a time interval T?

ConcepTest 11.1a ConcepTest 11.1a Harmonic Motion I 1) 0 2) A/2 3) A 4) 2A 5) 4A A mass on a spring in SHM has amplitude A and period T. What is the total distance traveled by the mass after a time interval T? time interval T complete oscillation The distance it covers is: A + A + A + A (4A). In the time interval T (the period), the mass goes through one complete oscillation back to the starting point. The distance it covers is: A + A + A + A (4A).

ConcepTest 11.2 ConcepTest 11.2 Speed and Acceleration 1) x = A 2) x > 0 but x < A 3) x = 0 4) x < 0 5) none of the above A mass on a spring in SHM has amplitude A and period T. At what point in the motion is v = 0 and a = 0 simultaneously?

ConcepTest 11.2 ConcepTest 11.2 Speed and Acceleration 1) x = A 2) x > 0 but x < A 3) x = 0 4) x < 0 5) none of the above A mass on a spring in SHM has amplitude A and period T. At what point in the motion is v = 0 and a = 0 simultaneously? If both v and a would be zero at the same time, the mass would be at rest and stay at rest! NO pointv a If both v and a would be zero at the same time, the mass would be at rest and stay at rest! Thus, there is NO point at which both v and a are both zero at the same time. Follow-up: Where is acceleration a maximum?

A mass oscillates in simple harmonic motion with amplitude A. If the mass is doubled, but the amplitude is not changed, what will happen to the total energy of the system? 1) total energy will increase 2) total energy will not change 3) total energy will decrease ConcepTest 11.5a ConcepTest 11.5a Energy in SHM I

A mass oscillates in simple harmonic motion with amplitude A. If the mass is doubled, but the amplitude is not changed, what will happen to the total energy of the system? 1) total energy will increase 2) total energy will not change 3) total energy will decrease The total energy is equal to the initial value of the elastic potential energy, which is PE s = ½kA 2. This does not depend on mass, so a change in mass will not affect the energy of the system. ConcepTest 11.5a ConcepTest 11.5a Energy in SHM I Follow-up: What happens if you double the amplitude?

A mass oscillates on a vertical spring with period T. If the whole setup is taken to the Moon, how does the period change? 1) period will increase 2) period will not change 3) period will decrease ConcepTest 11.7c ConcepTest 11.7c Spring on the Moon

A mass oscillates on a vertical spring with period T. If the whole setup is taken to the Moon, how does the period change? 1) period will increase 2) period will not change 3) period will decrease The period of simple harmonic motion only depends on the mass and the spring constant, and does not depend on the acceleration due to gravity. By going to the Moon, the value of g has been reduced, but that does not affect the period of the oscillating mass-spring system. ConcepTest 11.7c ConcepTest 11.7c Spring on the Moon Follow-up: Will the period be the same on any planet?

Two pendula have the same length, but different masses attached to the string. How do their periods compare? 1) period is greater for the greater mass 2) period is the same for both cases 3) period is greater for the smaller mass ConcepTest 11.8a ConcepTest 11.8a Period of a Pendulum I

Two pendula have the same length, but different masses attached to the string. How do their periods compare? 1) period is greater for the greater mass 2) period is the same for both cases 3) period is greater for the smaller mass The period of a pendulum depends on the length and the acceleration due to gravity, but it does not depend on the mass of the bob. T = 2  ( L / g ) ConcepTest 11.8a ConcepTest 11.8a Period of a Pendulum I Follow-up: What happens if the amplitude is doubled?

A grandfather clock has a weight at the bottom of the pendulum that can be moved up or down. If the clock is running slow, what should you do to adjust the time properly? 1) move the weight up 2) move the weight down 3) moving the weight will not matter 4) call the repair man ConcepTest 11.9 ConcepTest 11.9 Grandfather Clock

A grandfather clock has a weight at the bottom of the pendulum that can be moved up or down. If the clock is running slow, what should you do to adjust the time properly? 1) move the weight up 2) move the weight down 3) moving the weight will not matter 4) call the repair man The period of the grandfather clock is too long, so we need to decrease the period (increase the frequency). To do this, the length must be decreased, so the adjustable weight should be moved up in order to shorten the pendulum length. T = 2  ( L / g ) ConcepTest 11.9 ConcepTest 11.9 Grandfather Clock

ConcepTest 11.15aWave Motion I ConcepTest 11.15a Wave Motion I Consider a wave on a string moving to the right, as shown below. What is the direction of the velocity of a particle at the point labeled A ? 1) 2) 3) 4) 5) zero A

ConcepTest 11.15aWave Motion I ConcepTest 11.15a Wave Motion I Consider a wave on a string moving to the right, as shown below. What is the direction of the velocity of a particle at the point labeled A ? 1) 2) 3) 4) 5) zero The velocity of an oscillating particle momentarilyzero is (momentarily) zero at its maximum displacement. A Follow-up: What is the acceleration of the particle at point A?

Consider a wave on a string moving to the right, as shown below. What is the direction of the velocity of a particle at the point labeled B ? 1) 2) 3) 4) 5) zero B ConcepTest 11.15bWave Motion II ConcepTest 11.15b Wave Motion II

Consider a wave on a string moving to the right, as shown below. What is the direction of the velocity of a particle at the point labeled B ? 1) 2) 3) 4) 5) zero The wave is moving right to the right, so the particle at B has to moving upwards start moving upwards in the next instant of time. B ConcepTest 11.15bWave Motion II ConcepTest 11.15b Wave Motion II Follow-up: What is the acceleration of the particle at point B?

ConcepTest 11.19aStanding Waves I ConcepTest 11.19a Standing Waves I A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position b, the instantaneous velocity of points on the string: a b 1) is zero everywhere 2) is positive everywhere 3) is negative everywhere 4) depends on the position along the string

Observe two points: Just before b Just after b Both points change direction before and after b, so at b all points must have zero velocity. ConcepTest 11.19aStanding Waves I ConcepTest 11.19a Standing Waves I A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position b, the instantaneous velocity of points on the string: 1) is zero everywhere 2) is positive everywhere 3) is negative everywhere 4) depends on the position along the string

a b c ConcepTest 11.19bStanding Waves II ConcepTest 11.19b Standing Waves II A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position c, the instantaneous velocity of points on the string: 1) is zero everywhere 2) is positive everywhere 3) is negative everywhere 4) depends on the position along the string

direction depends on the location When the string is flat, all points are moving through the equilibrium position and are therefore at their maximum velocity. However, the direction depends on the location of the point. Some points are moving upwards rapidly, and some points are moving downwards rapidly. a b c ConcepTest 11.19bStanding Waves II ConcepTest 11.19b Standing Waves II A string is clamped at both ends and plucked so it vibrates in a standing mode between two extreme positions a and b. Let upward motion correspond to positive velocities. When the string is in position c, the instantaneous velocity of points on the string: 1) is zero everywhere 2) is positive everywhere 3) is negative everywhere 4) depends on the position along the string

If you fill your lungs with helium and then try talking, you sound like Donald Duck. What conclusion can you reach about the speed of sound in helium? 1) speed of sound is less in helium 2) speed of sound is the same in helium 3) speed of sound is greater in helium 4) this effect has nothing to do with the speed in helium ConcepTest 12.2c ConcepTest 12.2c Speed of Sound III

If you fill your lungs with helium and then try talking, you sound like Donald Duck. What conclusion can you reach about the speed of sound in helium? 1) speed of sound is less in helium 2) speed of sound is the same in helium 3) speed of sound is greater in helium 4) this effect has nothing to do with the speed in helium The higher pitch implies a higher frequency. In turn, since v = f, this means that the speed of the wave has increased (as long as the wavelength, determined by the length of the vocal chords, remains constant). ConcepTest 12.2c ConcepTest 12.2c Speed of Sound III Follow-up: Why is the speed of sound greater in helium than in air?

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position? 1) drops to 1/2 its original value 2) drops to 1/4 its original value 3) drops to 1/8 its original value 4) drops to 1/16 its original value 5) does not change at all ConcepTest 12.4a ConcepTest 12.4a Sound Intensity I

You stand a certain distance away from a speaker and you hear a certain intensity of sound. If you double your distance from the speaker, what happens to the sound intensity at your new position? 1) drops to 1/2 its original value 2) drops to 1/4 its original value 3) drops to 1/8 its original value 4) drops to 1/16 its original value 5) does not change at all distance doubles decrease to one-quarter For a source of a given power P, the intensity is given by I = P/4  r 2. So if the distance doubles, the intensity must decrease to one-quarter its original value. ConcepTest 12.4a ConcepTest 12.4a Sound Intensity I Follow-up: What distance would reduce the intensity by a factor of 100?

1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 12.5b ConcepTest 12.5b Decibel Level II

increase by 10 dB  increase intensity by factor of 10 1 (10) increase by 20 dB  increase intensity by factor of 10 2 (100) increase by 30 dB  increase intensity by factor of 10 3 (1000) 1) about the same 2) about 10 times 3) about 100 times 4) about 1000 times 5) about 10,000 times A quiet radio has an intensity level of about 40 dB. Busy street traffic has a level of about 70 dB. How much greater is the intensity of the street traffic compared to the radio? ConcepTest 12.5b ConcepTest 12.5b Decibel Level II Follow-up: What decibel level gives an intensity a million times greater?

(1) the long pipe (2) the short pipe (3) both have the same frequency (4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 12.6a ConcepTest 12.6a Pied Piper I

shorter pipe shorter wavelength frequency has to be higher A shorter pipe means that the standing wave in the pipe would have a shorter wavelength. Since the wave speed remains the same, the frequency has to be higher in the short pipe. (1) the long pipe (2) the short pipe (3) both have the same frequency (4) depends on the speed of sound in the pipe You have a long pipe and a short pipe. Which one has the higher frequency? ConcepTest 12.6a ConcepTest 12.6a Pied Piper I

1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 12.7 ConcepTest 12.7 Open and Closed Pipes

open pipe½ of a wave closed pipe ¼ of a wave wavelength is larger in the closed pipefrequency will be lower In the open pipe, ½ of a wave “fits” into the pipe, while in the closed pipe, only ¼ of a wave fits. Because the wavelength is larger in the closed pipe, the frequency will be lower. 1) depends on the speed of sound in the pipe 2) you hear the same frequency 3) you hear a higher frequency 4) you hear a lower frequency You blow into an open pipe and produce a tone. What happens to the frequency of the tone if you close the end of the pipe and blow into it again? ConcepTest 12.7 ConcepTest 12.7 Open and Closed Pipes Follow-up: What would you have to do to the pipe to increase the frequency?

Observers A, B and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points ConcepTest 12.11a ConcepTest 12.11a Doppler Effect I

Observers A, B and C listen to a moving source of sound. The location of the wave fronts of the moving source with respect to the observers is shown below. Which of the following is true? 1) frequency is highest at A 2) frequency is highest at B 3) frequency is highest at C 4) frequency is the same at all three points observer C The number of wave fronts hitting observer C per unit time is greatest -- thus the observed frequency is highest there. ConcepTest 12.11a ConcepTest 12.11a Doppler Effect I Follow-up: Where is the frequency lowest?

You are heading towards an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear ? 1) lower than f 0 2) equal to f 0 3) higher than f 0 ConcepTest 12.11b ConcepTest 12.11b Doppler Effect II

You are heading towards an island in a speedboat and you see your friend standing on the shore, at the base of a cliff. You sound the boat’s horn to alert your friend of your arrival. If the horn has a rest frequency of f 0, what frequency does your friend hear ? 1) lower than f 0 2) equal to f 0 3) higher than f 0 approach of the source frequency is shifted higher Due to the approach of the source towards the stationary observer, the frequency is shifted higher. This is the same situation as depicted in the previous question. ConcepTest 12.11b ConcepTest 12.11b Doppler Effect II

In the previous question, the horn had a rest frequency of f 0, and we found that your friend heard a higher frequency f 1 due to the Doppler shift. The sound from the boat hits the cliff behind your friend and returns to you as an echo. What is the frequency of the echo that you hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 but lower than f 1 4) equal to f 1 5) higher than f 1 ConcepTest 12.11c ConcepTest 12.11c Doppler Effect III

In the previous question, the horn had a rest frequency of f 0, and we found that your friend heard a higher frequency f 1 due to the Doppler shift. The sound from the boat hits the cliff behind your friend and returns to you as an echo. What is the frequency of the echo that you hear? 1) lower than f 0 2) equal to f 0 3) higher than f 0 but lower than f 1 4) equal to f 1 5) higher than f 1 you are now a moving observer approaching the sound wave even higher frequency The sound wave bouncing off the cliff has the same frequency f 1 as the one hitting the cliff (what your friend hears). For the echo, you are now a moving observer approaching the sound wave of frequency f 1 so you will hear an even higher frequency. ConcepTest 12.11c ConcepTest 12.11c Doppler Effect III