I have Honors in Physics and am a qualified teacher, but I've taken 4 yrs out to have kids. I'm trying to get back into it by starting with tutoring, and I am totally perplexed by this solution to the question, so think there is a fault with it. The book is a new edition so it is possible. I'm going nuts that I can't solve it!(adsbygoogle = window.adsbygoogle || []).push({});

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

If the speed of sound in air is 346ms^-1, at what speed would the sound from a fire truck siren appear to be travelling in the following situations?

a) You are driving towards the stationary fire truck at 30ms^-1

b)You are driving away from the stationary truck at 40m/s

c)You are stationary ant the fire truck is heading towards you at 20m/s

d)You are driving at 30m/s and about to overtake the fire truck, which is travelling at 20m/s in the same direction.

2. Relevant equations

i

None - it comes under the 'relativity' section and the student is not supposed to have studied the doppler effect yet, although there is a paragraph that stated, "If you are moving towards a source of sound, the speed of sound will be the sum of the speed of sound and your own speed"

3. The attempt at a solution

So (a) and (b) are easy to answer - 376m/s and 306m/s respectively, BUT (c) and (d) are beyond me!

(c) solution given is 346m/s - is that because "I" am stationary?

(d) solution given is 376m/s - it that because you only look that "I" am moving at 30m/s and you ignore the moving truck?

It just doesn't make any sense to me - esp when you take into account doppler effect. If anyone can explain it rather than just fudging the the explaination to fit the solutions I would be able to sleep much better!

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

2. Relevant equations

3. The attempt at a solution

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# Could there be a mistake in the textbook solutions?

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