Short Answer
3: C
4: D
Problem Three
Remark
Somewhere we ought to be told that this is the Doppler Effect. I have never done a problem using this formula, so I think I'm doing it correctly, but no guarantees. My guess is that the frequency increases as it comes towards you and decreases as it moves away from you. I think that is correct.
Formula
<em><u>Givens</u></em>
- f' = observed frequency
- f = actual frequency
- v = velocity of sound or light waves.
- vo = velocity of observer (in both cases 0)
- vs = velocity of source.
f' = (v + vo) * f / (v - vs)
Solution
- v = 3*10^8 m/s
- f' = 1.1 f
- f = f
- vo = 0 We are standing still while all this is going on.
- vs = ???
f'/f = 1.1
1.1 = (3*10^8 + 0 ) / (3*10^8 - vs)
3.3*10^8 - 1.1*vs = 3*10^8
3.3*10^8 - 3*10^8= 1.1 vs
0.3 * 10^8 = 1.1 vs
2.73 * 10^7 = vs
The closest answer is 3.00 * 10^7 which is C
Problem Four
Here what is happening is that you are looking for the frequency resulting from a wave moving towards you at 1/2 the speed of sound. You are not moving.
<em><u>Givens</u></em>
- v = v
- vs = 1/2 v
- f ' = ?
- f = 1000 hz
- vo =0
f' = v/(v - 1/2v) * 1000
f' = v/ (1/2 v) * 1000
f' = 2 * 1000
f' = 2000 which is D
