Posted by **PLEASE HELP!!** on Thursday, February 3, 2011 at 8:58pm.

While blowing its horn of frequency 477 Hz, a car accelerates at 0.94 m/s2.

The car starts from rest by your side and moves away.

How many seconds does it take for the frequency you hear to decrease by 5%?

Hint: Do not forget to include the time it will take for sound to reach you.

*Im getting an answer of about 20, but i don't want to submit my homework yet, can someone please check it over to see if i am correct?*

- physics -
**Henry**, Sunday, February 6, 2011 at 12:23pm
F = ((V + Vr) / (V + Vs))Fo = 0.95*477.

((343 + 0) / (343 + Vs))477 = 453.15,

(343 / (343 + Vs))477 = 453.15 Hz,

163611 / (343 + Vs) = 453.15,

Cross multiply:

155430.45 + 453.15Vs = 163611

453.15Vs=163611 - 155430.45 = 8180.55,

Vs = 8180.55 / 453.15 = 18.05m/s.

Vf = Vi + at = 18.05m/s.

0 + 0.94t = 18.05,

t = 18.05 / 0.94 = 19.2s to reach final velocity.

d = Vi*t + 0.5at^2,

d = 0*19.2 + 0.5 * 0.94 * (19.2)^2,

d = 0 + 173.26m = 173.2m after final velocity.

d = V*t,

t = d / V = 173.2m / 343m/s = 0.50s to

reach receiver(you).

t(tot.) = 19.2 + 0.5 = 19.7s

So our answers are about the same.

## Answer This Question

## Related Questions

- physics - While blowing its horn of frequency 466 Hz, a car accelerates at 0.84 ...
- Physics - Frequency - While blowing its horn of frequency 580 Hz, a car ...
- Physics - While blowing its horn of f=524 Hz a car accelerates at 0.8m/s^2 the ...
- Physics - Frequency - This is in reply to a previous post, I'm not really sure ...
- physics - 1)As a sound source moves away from a stationary observer, the number ...
- physics - 1)As a sound source moves away from a stationary observer, the number ...
- physics - a car sounds its horn as it travels at a steady speed of 15m/s along a...
- physics - 1)As a sound source moves away from a stationary observer, the number ...
- physics..please help? - At rest, a car’s horn sound at the note A(440Hz) The ...
- Physics - A car starts from rest and accelerates unifomly at 3m/s^2. A second ...

More Related Questions