Answers
5: A
6: C
Problem 5
Frequency and wavelength have an inverse relationship. As the frequency increases, the wavelength will decrease. You should really study the way the Doppler effect looks as a siren (for example) comes towards you. You can google it to find diagrams. The waves move closer and closer together as the siren heads towards the observer. Wavelength down, frequency up.
Which answer says that? Looks like A to me.
Problem 6
Givens
- The speed of sound is 343 m/s about.
- The speed of the train is 25 km / hour
- The observer isn't moving
- The original frequency is 400 Hz
- The final frequency is ?????
f' = f * (v / v - vs)
f' = 400 * (343 / (343 - 25) )
f' = 400 * 1.0786
f' = 431
v = lambda (wavelength) * f
f = 431
λ = ???
v = 343 m/s
v = λ * f
343 = λ * 431
343 / 431 = 0.795 m
Looks like the answer to this is C
