Answer:
Doppler effect.
Explanation:
The velocity of the moving car affects the wavelengths of the reflecting radio waves according to the principle of Doppler effect. Therefore, for a car moving away from the radar gun, the wavelength of the radio waves is increased, and for a car moving towards the gun, the wavelength is decreased. The degree of increase or decreases depends on the speed of the car, so if you know how much a wavelength has changed, you know the velocity of the car.
Concave mirrors can make a real image.when the object is away from the mirror it is called real image and when the object is closer to the mirror it is called virtual mirror.
The gravitational force acting between them is 
Data given;
- M1 = 45kg
- M2 = 11kg
- r = 2.0m
- G =

To solve this question, we need to apply gravitational force or energy formula.
<h3>Gravitational Force</h3>
This states that the force of attraction between two bodies is equal to the product of their bodies and inversely proportional to the square of their distance apart.
Mathematically;

let's substitute the values and solve

The force of gravity acting between them is 
Learn more on gravitational force here;
brainly.com/question/11359658
Answer:
2.25m/s
Explanation:
wavelength=4.5m
period=2sec
frequency= 1/period
=1/2
speed= wavelength×wave frequency
=4.5×1/2
=2.25 m/s
so, none of the options are correct