Thursday
July 24, 2014

Homework Help: physics

Posted by Liz on Saturday, August 21, 2010 at 1:57pm.

A speeding car is pulling away from a police car. The police car is moving at 30 m/s. The radar gun in the police car emits an electromagnetic wave with a frequency of 20.0 x 10^9 Hz. The wave reflects from the speeding car and returns to the police car where the frequency is measured to be 4750 Hz less than what was emitted. The speed of light is 3 x 10^8 m/s. How fast is the speeding car going?

I know you have to set up two equations (one for before the bounce off the speeding car and one after), but I can't seem to work it to a reasonable number.

The equation is:
fd=(vvd)/(vvs)fs

where fd= frequency recieved by a detector
fs= frequency of source
v= velocity of the wave
vd= velocity of the detecor
vs= velocity of the source

I've been working on it for days, but the best thing I've gotten was that the car was traveling at 101 m/s, which doesn't sound possible to me lol. Could anyone look at this and explain to me what I'm doing wrong?

Answer this Question

First Name:
School Subject:
Answer:

Related Questions

Physics - Suppose that a police car on the highway is moving to the right at 27 ...
Physics help! - Suppose that a police car on the highway is moving to the right ...
physics - Suppose that a police car on the highway is moving to the right at 26...
physics please help!! - Suppose that a police car on the highway is moving to ...
Physics - Suppose that a police car on the highway is moving to the right at 20 ...
Physics - Suppose that a police car on the highway is moving to the right at 20 ...
PHYSICS-URGENT HELP - A stationary police car emits a sound of frequency 1200 Hz...
Physics - A speeding car is traveling at a constant 30.0 m/s when it passes a ...
Physics - A speeding car is traveling at a constant 30.0 m/s when it passes a ...
Physics - A police car is traveling east at 40.0 m/s along a straight road, ...

Search
Members