Answer:
The beats frequency measures approximately
4.4 kHz
Explanation:
The beat frequency arises from the original ultrasound frequency,
, and the frequency of the sound reflected off the car,
:
(1)
To calculate the frequency of the reflected sound, we apply the Doppler effect formula:

where
v = 340 m/s, the speed of sound
is the velocity of the car
is the frequency of the sound emitted
By substituting values,

Thus, the beat frequency (1) is

Answer:

Explanation:
In this scenario, we determine the initial velocity as follows:

The final velocity in this instance can be expressed as:

It is noted that transitioning from 7m/s to 13m/s takes 8 seconds. We can apply a specific kinematic equation to find the acceleration for the first part of the journey:

Solved for acceleration, we find:

For the subsequent route, we assume constant acceleration and that the train continues for 16 seconds, beginning with an initial velocity of 13m/s from the previous segment, allowing us to calculate the final speed via the following formula:

Substituting into the equation yields:

We will utilize Wien's displacement law, given by the equation λ T = b, where λ represents the wavelength of emitted light from a heated object at maximum. By substituting the provided temperature and constant b into the equation, we find λ for various temperatures: at 500 K, λ = 5.796 μm or 5796 nm; at 1050 K, λ = 2760 nm; at 1800 K, λ = 1610 nm; and at 2500 K, λ = 1159.2 nm. The visible light spectrum starts at 740 nm, suggesting that at 2500 K, some visible red light may emerge as its calculated peak wavelength is within the visible range.