# Homework Help: Pulse Question

1. Jan 30, 2016

### OmniNewton

1. The problem statement, all variables and given/known data

2. Relevant equations
Refer to 3.

3. The attempt at a solution
My problem is the theory I am unsure how any equations apply to this problem. This seems bad that I have no attempt at solution but I am honestly unsure how to start or of any relevant equations.

2. Jan 31, 2016

### ehild

Think instead of looking after equations. Imagine, you stand at distance d from a wall, and you clap once. The sound reflects from the wall. What time after the clap does the echo reach you?

3. Jan 31, 2016

### OmniNewton

v=dt
so t = v/2d

4. Jan 31, 2016

### ehild

You mean the time is the shorter the longer is the distance ???
And what is the time if the wall is at distance d+w?
What is the difference of times if one wall is at distance d and the other wall is w distance farther?

5. Jan 31, 2016

### OmniNewton

Sorry about the delay I've been really thinking this through. I'm just unsure what is being said by difference of times.

6. Jan 31, 2016

### ehild

The first of your problem is how do you get the time you need to cover a distance d with speed v. You travel with speed 100 km/h, what time is needed to reach a town at 200 km distance?

7. Jan 31, 2016

### OmniNewton

2 hours

8. Jan 31, 2016

### ehild

What is the general formula used to get time from distance and speed?

9. Jan 31, 2016

### OmniNewton

d=vt
t = d/v

10. Jan 31, 2016

### ehild

It is correct now. In what time does the echo of the clap return from a wall at distance d? And what is the time of return from a wall at distance d+w?

11. Jan 31, 2016

### UchihaClan13

The time taken to return back(when the distance is d)
is equal to 2d/v where v is the velocity of sound
and when the distance is d+w
The time taken is 2(d+w)/v
Therefore
The difference in the times taken equals 2w/v

12. Jan 31, 2016

### OmniNewton

Alright after looking at Uchiha's work that is correct. difference in time represents the period.

So,

f = 1/T = v/2w = 343 m/s/2(0.75m) = 230 Hz

for b) since f is proportional to 1 /w the frequency will be higher

13. Jan 31, 2016

### UchihaClan13

Precisely,OmniNewton
Just some thinking and calculations always suffice :)

14. Jan 31, 2016

### OmniNewton

Thank You So Much!

15. Jan 31, 2016

### UchihaClan13

You're welcome!

16. Jan 31, 2016

### UchihaClan13

Heh thanks mate for those likes!:)