Doppler Effect involving two moving objects

In summary, the problem involves a truck and a police car with different velocities and the frequency of a siren. Using the equation f'=(v+vo)/(v-vs)f, we can solve for the frequency heard by an observer in the truck as the police car approaches. However, it is important to consider the signs of the velocities to get the correct answer.
  • #1
sloane729
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Homework Statement


A truck moving at 36 m/s is overtaken by a police car moving at 45 m/s in the same direction. If the frequency of the siren relative to the police car is 500 Hz, what is the frequency heard by an observer in the truck as the police car approaches the truck? (The speed of sound in air is 343 m/s.)

Homework Equations


f'=(v+vo)/(v-vs)f

vo = velocity of the truck
vs = velocity of the police car

The Attempt at a Solution


I thought this would be a simple substitution problem but it's obviously not if I'm getting a different a wrong answer

f' = (343+36)/(343-45)(500) = 636Hz (This is my answer which was marked wrong)

Please advise
 
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  • #2
Think through the signs. The two vehicles do not have 36+45 m/s relative speed.
 

FAQ: Doppler Effect involving two moving objects

1. What is the Doppler Effect?

The Doppler Effect is a phenomenon where the frequency of a wave appears to change when the source of the wave or the observer is in motion.

2. How does the Doppler Effect apply to two moving objects?

In the case of two moving objects, the Doppler Effect occurs when both the source and the observer are in motion relative to each other, causing a change in the frequency of the wave.

3. What factors affect the Doppler Effect in two moving objects?

The factors that affect the Doppler Effect in two moving objects include the speed of the objects, the distance between them, and the angle of their relative motion.

4. How is the Doppler Effect used in real life?

The Doppler Effect is used in various real-life applications such as in weather radars, medical ultrasound technology, and police radar guns. It is also used to measure the speed and distance of stars and galaxies in astronomy.

5. Can the Doppler Effect be observed in sound and light waves?

Yes, the Doppler Effect can be observed in both sound and light waves. It is commonly experienced when a siren or a train passes by, as the pitch of the sound appears to change. In astronomy, it is used to determine the movement of celestial bodies based on the shift in their light frequencies.

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