Question 490: Waves

Question

A speeding motorcyclist sees traffic jam ahead him. He slows down to 36 km hour$$-$$1. He finds that traffic has eased and a car moving ahead of him at 18 km hour$$-$$1 is honking at a frequency of 1392  Hz. If the speed of sound is 343 m s$$-$$1, the frequency of the honk as heard by him will be

Accepted Answer

Here, speed of motorcyclist, v
m
= 36 km hour
Ã¢ÂÂ1
$$ = 36 	imes {5 \over {18}} = 10m{s^{ - 1}}$$
Speed of car,
$${v_c} = 18\,km\,hou{r^{ - 1}} = 18 	imes {5 \over {18}}m{s^{ - 1}} = 5m{s^{ - 1}}$$
Frequency of source, $${\upsilon _0}$$ = 1392 Hz
Speed of sound, v = 343 m s
Ã¢ÂÂ1
The frequency of the honk heard by the motorcyclist is
$$v' = {\upsilon _0}\left( {{{v + {v_m}} \over {v + {v_C}}}} ight) = 1392\left( {{{343 + 10} \over {343 + 5}}} ight)$$
$$ = {{1392 	imes 353} \over {348}} = 1412\,Hz$$

Answer

1332 Hz

Answer

1372 Hz

Answer

1412 Hz

Answer

1454 Hz

Waves

A speeding motorcyclist sees traffic jam ahead him. He slows down to 36 km hour$-1. He finds that traffic has eased and a car moving ahead of him at 18 km hour-1 is honking at a frequency of 1392 Hz. If the speed of sound is 343 m s-$1, the frequency of the honk as heard by him will be

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