Physics, 06.10.2019 08:30 diamondalize21p84czi

Acar is stopped at a traffic light. when the light turns green, the car starts from rest with an acceleration of 2.5 m/s2 . also, as the light turns green, a truck traveling with a constant velocity of 10 m/s passes the car. the truck’s horn is stuck, emitting sound at a frequency of 440hz. what frequency of sound is heard by the driver of the car, (a) 5 seconds before the light turned green? (b) 5 seconds after the light turned green? (c) 10 seconds after the light turned green?

Answers: 2

Show answers

Answers

Answer from: jamalnellum56

Doppler effect is used to find the change in wave frequency when either the observer or source or both are moving

(a) 5 seconds before the light turned green, the frequency of sound heard by the observer is 453. $\overline {213}$ Hz

(b) 5 seconds after the light turned green the frequency of the sound heard by the observer is approximately 443.12 Hz

The reason the above values are correct is given as follows;

The given parameters are;

Initial velocity of the car = 0 (Starts from rest)

Acceleration of the car, a = 2.5 m/s²

The constant velocity of the truck that passes the car, v_s = 10 m/s

Frequency of the sound emitted by the truck, f = 440 Hz

(a) The frequency of the sound heard by the driver of the car 5 seconds before the light turns green is given as follows;

The Doppler shift formula is given as follows;

$f' = \dfrac{v }{v - v_s} \times f$

Where;

v = The speed of sound in air ≈ 343 m/s

Therefore;

$f' = \dfrac{343}{343 - 10} \times 440 \approx 453.\overline{213}$

The frequency of sound heard by the observer, f' = 453. $\overline {213}$ Hz

(b) The speed of the car t = 5 seconds after the light turns green is given as follows;

v = u + a·t

∴ v = 0 + 2.5 × 5 = 12.5

The speed of the car, 5 seconds after the light turns green, v_0 = 12.5 m/s

The position of the car at 5 seconds after the light turns green is given as follows;

$s = u\cdot t + \dfrac{1}{2} \cdot a \cdot t^2$

u = 0

$\therefore s = \dfrac{1}{2} \times 2.5 \times 5^2 = 31.25$

The position of the truck after 5 seconds = 5 s × 10 m/s = 50 m

Therefore, the car is moving towards the truck, which is moving away from the car

The correct formula to use is therefore;

$f' = \dfrac{v + v_0}{v + v_s} \times f$

$f' = \dfrac{343 + 12.5}{343 + 10} \times 440 \approx 443.12$

The frequency of the sound heard by the driver, f' ≈ 443.12 Hz

v = 0 + 2.5 × 10 = 25

The velocity of the car = 25 m/s

The position of the car, s₁₀, is given as follows;

$s_{10} = \dfrac{1}{2} \times 2.5 \times 10^2 = 125$

The position of the car, s₁₀ = 125 m

The position of the truck, d₁₀ = 10 s × 10 m/s = 100 m

Therefore, the car is ahead of the truck, and the equation to be used is therefore;

$f' = \dfrac{v - v_0}{v - v_s} \times f$

Which gives;

$f' = \dfrac{343 - 25}{343 - 10} \times 440 \approx 420.\overline{180}$

The frequency of the sound heard by the driver, f' = 420. $\overline{180}$ Hz

Learn more about the Doppler effect here:

link

Answer from: Quest

i guess it’s a and b

For which optical devices does d sometimes have a positive value

Answer from: Quest

English can you write this in english do we can you

Another question on Physics

Physics, 21.06.2019 19:30

Molten iron fills a mould, which has a volume of 200 cm cubed. calculate the volume when the iron cools and solidifies. molten iron has a density of 7.0g/cm cubed. in its solid state, iron has a density of 8.0g/cm cubed.

Answers: 3

Answer

Physics, 22.06.2019 09:50

Which statement correctly describes the current in a circuit that is made up of any two resistors connected in parallel with a battery? a. the current in the battery and in each resistor is the same b. the current the battery equals to the sum of the currents in the resistors c.the current in the battery is less than the current in either resistor d. the current in the battery equals to the product of the currents in the resistors

Answers: 1

Answer

Physics, 22.06.2019 11:30

Why is the energy that results from a roller coaster's position at the top of a hill referred to as potential energy?

Answers: 1

Answer

Physics, 22.06.2019 22:40

Is a copper wire a conductor or insulator?

Answers: 2

Answer

You know the right answer?

Acar is stopped at a traffic light. when the light turns green, the car starts from rest with an acc...