Question

Can someone answer these?

Answer 1

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

Givens

• 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.

Givens

• 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