# 2 Sound waves reflection easy problems

1. Oct 2, 2016

### Clara Chung

1. The problem statement, all variables and given/known data
Refer to the photos, question 21 and 22(the one with a helicopter)

2. Relevant equations

3. The attempt at a solution
for question 21, if the counts to ten, there are 9 intervals. I divide 20 by 9 and divide it again by 2 and get 1.1s not 0.5s.
for question 22. I think it is C. Because the first reflected pulse has travelled 2h and the second reflected pulse has travelled 4h. I think it is impossible for the answer to be A, the pulse should travel slower in water.

File size:
28.8 KB
Views:
28
File size:
40 KB
Views:
19
2. Oct 2, 2016

### lewando

For Q21, if the first clap is associated with the count of zero, wouldn't there be 10 intervals?
For Q22, the speed of sound in water is greater than the speed of sound in air.

3. Oct 2, 2016

### Clara Chung

But 20/10(2) = 1s?

4. Oct 2, 2016

### lewando

That is true. That result matches answer B. I can't see how A could be correct.

5. Oct 2, 2016

### lewando

Actually I misread the question. Only claps are being counted.

6. Oct 2, 2016

### Clara Chung

Oh thanks I can do it now