To solve this problem we will apply the concepts related to the Doppler effect. The Doppler effect is the change in the perceived frequency of any wave movement when the emitter, or focus of waves, and the receiver, or observer, move relative to each other. Mathematically it can be described as

Here,
=frequency received by detector
=frequency of wave emitted by source
=velocity of detector
=velocity of source
v=velocity of sound wave
Replacing we have that,


Therefore the frequencty that will hear the passengers is 422Hz
Answer:
Spring constant of the spring will be equal to 9.255 N /m
Explanation:
We have given mass m = 0.683 kg
Time taken to complete one oscillation is given T = 1.41 sec
We have to find the spring constant of the spring
From spring mass system time period is equal to
, here m is mass and K is spring constant
So 

Squaring both side


So spring constant of the spring will be equal to 9.255 N /m