A man strikes a 460. Hz tuning fork and moves away from you

[Student3.41]

Homework Statement

A man strikes a 460. Hz tuning fork and moves away from you and towards the blackboard at a constant velocity of 3.80 m/s. What beat frequency do you hear if the velocity of sound on that day is 340 m/s?

Homework Equations

The Attempt at a Solution

Since the source is moving away from a stationary observer, we write;

f_o= (1/1+V_s/V) * f_s

f_o= (1/1.011)(460Hz)
f_o= 455Hz

SO, f_o= 455Hz, f_s=460Hz

Now we find the beat frequency, we write;

f_beat= |f₁-f₂|=5.00Hz (This was wrong)


---> Not sure what I am missing.. please help. Thanks

 

[Student3.41]

Noone?

 

[thst1003]

You had everything right. Except the sign on the bottom. Given the fact that the source is moving TOWARDS the observer the sign on the bottom should be negative whereas you have it positive. That should make the difference...

 

[Student3.41]

You had everything right. Except the sign on the bottom. Given the fact that the source is moving TOWARDS the observer the sign on the bottom should be negative whereas you have it positive. That should make the difference...

"moves away from you and towards the blackboard ", so the source being the teacher is not moving towards you(observer) he is moving away from the observer in this problem... Even if he was moving towards you that still equals 465Hz which would result in a 5.0Hz beat frequency.

 

[thst1003]

You are right. I overlooked that. I am betting that your answer is correct. The difference could possibly attributed to the fact that the speed of sound can vary. Sorry about my incorrect answer.

 

[Student3.41]

i actually had to find two frequencies using too different equations because the sound bounces off the black board and moves towards the observer. Also, when he moves away from the observer. Solved them equations and found the beat frequency

 

[thst1003]

Perhaps you need to calculate something dealing with the speed of sound... I can't remember this stuff. It was a while ago.