The speed of sound is 343 m/s. A car’s horn produces a frequency of 400 Hz when

Question

The speed of sound is 343 m/s. A car’s horn produces a frequency of 400 Hz when at rest. If the car is traveling West at 30 m/s toward an observer, what velocity must an observer have to hear a frequency of 400 Hz. (You must indicate both speed and direction. Indicate direction with words. Do not just use a sign.)

The index of refraction for air and water are 1.0 and 1.33 respectively.

a) If light comes from air and hits at an incident angle of 70°, what is the angle of reflection?

b) If light comes from air and hits at an incident angle of 70°, what is the angle of refraction?

c) If light comes from water and hits at an incident angle of 70°, what is the angle of refraction?

Explanation / Answer

1) the obsorver should have 30 m/s velocity towards west.

2)

a) angle of reflection = angle of incidence

= 70 degrees

b) Apply Snell's law

sin(theta_i)/sin(theta_r) = n2/n1

sin(70)/sin(theta_r) = 1.33/1

sin(theta_r) = sin(70)/1.33

theta_r = sin^-1(0.582)

= 35.6 degrees

c)

Total internal reflection takes place.

so, there is no refracted ray.

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