Q6.7
You would also need to know the speed of sound.
Q6.17
Time the echo, divide by two (since this is the round trip time), and then use d = vt.
Q6.22
Without diffraction, the waves would not spread out, and would therefore never overlap. No overlap means no interference.
Q6.23
The sound gets louder and softer repeatedly, as you move from positions of constructive interference to destructive interference.
P6.20
P6.24
P6.25
P6.26
