Question

A police car parked on the side of the highway emits a 1200 Hz sound that bounces off a vehicle farther down the highway and returns with a frequency of 1250 Hz. How fast is the vehicle going?
a. 8.9
b. 6.9
c. 6.5
d. 5.6

Answer 1

Answer: 1. B) 2120 Hz

2. A) 7.7 m/s

3. B) 6.9 m/s

4. C) 0.80 m; 431 Hz

5. A) 2186 Hz

6. A) the frequency of the siren is higher and the wavelength is shorter than it was at first

7. C) 300 x 10^7 m/s

8. A) 1500 Hz

9. D) 2000 Hz

10. D) 780 m/s

Explanation: 100% physics lesson 2 :)

Answer 2

f' = frequency observed by the police car after sound reflected from the vehicle and comes back to police car = 1250 Hz

f = frequency emitted by the police car  = 1200 Hz

V = speed of sound = 340 m/s

v = speed of vehicle = ?

frequency observed by the police car is given as

f' = f (V + v)/(V - v)

inserting the values in the above equation

1250 = 1200 (340 + v)/(340 - v)

v = 6.9 m/s