conceptual questions physics exam 3

8. Pendulum clocks are made to run at the correct rate by adjusting the pendulum's length. Suppose you move from one city to another where the acceleration due to gravity is slightly greater, taking your pendulum clock with you, will you have to lengthen or shorten the pendulum to keep the correct time, other factors remaining constant? Explain your answer.

lengthen it

3. Why is the index of refraction always greater than or equal to 1?

using the equation -the speed of light is maximum in a vacuum and always less than c in any other medium , so its always greater than or equal to 1. numerator greater than denominator

6. Due to efficiency considerations related to its bow wake, the supersonic transport aircraft must maintain a cruising speed that is a constant ratio to the speed of sound (a constant Mach number). If the aircraft flies from warm air into colder air, should it increase or decrease its speed? Explain your answer.

the energy of atoms increases with increase in temperature. sound travels faster in warm air because of the high energy the atom has, its easy for the sound wave to propagate through warm medium. the speed of sound decreases as temperature decreases, so the plane should go slower

13. Why are soldiers in general ordered to "route step" (walk out of step) across a bridge?

their marching frequency can match with the vibrational frequency of the bridge (resonance frequency) and will amplify the osciallation amplitude of the bridge and can cause the bridge to collapse if the mechanical resonance of the bridge isn't strong enough

7. Some people modify cars to be much closer to the ground than when manufactured. Should they install stiffer springs? Explain your answer.

yes,

11. How would a car bounce after a bump under each of these conditions? -overdamping -underdamping -critically damp

-car bounces to a visibile extent and takes a longer time to return to the equilibrium position -doesn't bounce as much as overdamped . comes to equilibrium state faster , it may overshoot . comes back after 2-3 times -attains equilibrium state very quickly with no oscillations. may miss once but comes back and gets it

2. When sound passes from one medium to another where its propagation speed is different, does its frequency or wavelength change? Explain your answer briefly.

-frequency is independent from speed of sound, so if vw changes, the wavelength changes

15. What is the difference between propagation speed and the frequency of a wave? Does one or both affect wavelength? If so, how?

-propogation speed is the speed at which the disturbance in medium (wave) moves -wave frequency- the number of cycles of that wave per second -look at equation

14. Give one example of a transverse wave and another of a longitudinal wave, being careful to note the relative directions of the disturbance and wave propagation in each.

-transverse= electromagnetic -longitudinal=sound

10. Give an example of a damped harmonic oscillator. (They are more common than undamped or simple harmonic oscillators.)

Damped harmonic motion is when the amplitude of the oscillation gradually decreases and the system comes to rest due to the action of dissipative forces. A simple pendulum suspended in air is an example of damped harmonic oscillator.

2. What conditions must be met to produce simple harmonic motion?

F net must be pointing in the opposite direction of the displacement (always points in the center position) -Fnet is always directly proportional to the displacement

9. You are given two wind instruments of identical length. One is open at both ends, whereas the other is closed at one end. Which is able to produce the lowest frequency?

Standing wave resonances in pipes have some interesting properties. If one end of the pile is closed, that end must have a "node" when sounding a resonance. If an end of a pipe is open, it must have an "anti-node." In the case of a pipe closed at one end, the lowest frequency resonance happens when you have just this situation, a single node at the closed end and an anti-node at the other end. The wavelength of this sound is four times the length of the pipe. We call this a quarter-wave resonator. In the case of a pipe opened at both ends, the lowest frequency resonance has one node in the center and anti-nodes at each end. This is a half-wave resonance; half of the wavelength is contained in the pipe. If this pipe is the same length as the closed pipe, the frequency of this resonance will be twice that of the closed pipe.

7. When you hear a sonic boom, you often cannot see the plane that made it. Why is that?

a sonic boom is made when the sound sources speed exceeds the speed of sound. the aircraft passes the observer before the sonic boom reaches the observer. the speed of the plane is greater than the speed of sound

if it goes from small to larger n=

bends near the normal

9. Explain in terms of energy how dissipative forces such as friction reduce the amplitude of a harmonic oscillator. Also explain how a driving mechanism can compensate. (A pendulum clock is such a system.)

in the case of harmonic motion, the law of conservation of energy is obeyed and the amplitude of the system remains constant. dissipative forces remove energy resulting in a decrease in amplitude after every osciallation since the sum of KE and PE decrease after every oscillation. -for driving mechanism, the driving force is taken into account. The energy lost due to dissipative forces can be provided back into the system with the involvement of the driving force compensating the energy lost due to dissipative force

8. How does an unamplified guitar produce sounds so much more intense than those of a plucked string held taut by a simple stick?

plucking the string of a guitar generates a wave that travels to the fixed end of the string. the waves are reflected back and interfere constructively with the source wave. this increases the amplitude of the sound wave. -I=square of the amplitude of the sound. the amplitude of the sound is larger than amplitude from a taut string. the sound produced from an unamplified guitar has high intensity

4. Does the fact that the light flash from lightning reaches you before its sound prove that the speed of light is extremely large or simply that it is greater than the speed of sound? Discuss how you could use this effect to get an estimate of the speed of light.

since the distance traveled by light and sound are the sae=me, it means that the speed of light is much quicker than the speed of sound. the equation

6. As you pass a freight truck with a trailer on a highway, you notice that its trailer is bouncing up and down slowly. Is it more likely that the trailer is heavily loaded or nearly empty? Explain your answer.

slowly bouncing is a low frequency -k should be constant , the larger the m the lower frequency