Question

5. A man in a car is listening to the radio. The radio station is broadcasting at a frequency of 85 MHz from two radio transmitters immediately behind and immediately in front of the car. At 11.30 am he has excellent reception, but 15 minutes later is has terrible reception. How fast is the car going

Answer 1

Speed = 0.00392 m/s

Step-by-step explanation:

Solution:

Frequency of the radio = 85 MHz

If we have the frequency, we can calculate the wavelength of the radio wave.

As we know,

Frequency = speed of light/wavelength

wavelength = c/f

c = speed of light = 3 x
`10^(8)` m/s

So,

Wavelength = 3 x
`10^(8)` m/s / 85 x
`10^(6)` Hz

Wavelength = 3.5294 m

Man gets disturbed reception at t = 15 min

t = 15 x 60 = 900 s

t = 900 s

Speed = distance/time

Here, distance is wavelength. So,

Speed = 3.5294 m / 900 s

Speed = 0.00392 m/s

Hence, the man's car is going with speed of 0.00392 m/s