<h2>Answer: True
</h2>
The <u>Doppler effect</u> refers to the change in a wave perceived frequency when the emitter of the waves, and the receiver (or observer in the case of light) move relative to each other.
In other words, it is the variation of the frequency of a wave due to the relative movement of the source of the wave with respect to its receiver.
It should be noted that this effect bears its name in honor of the Austrian physicist <u>Christian Andreas Doppler</u>, who in 1842 proposed the existence of this effect for the case of light in the stars. Another important aspect is that the effect occurs in all waves (including light and sound). However, it is more noticeable to humans with sound waves.
Mass of the displaced material. In water it would be the mass of the water that the volume of the ball displaces.
The force is -12,000 N
Explanation:
First of all, we calculate the acceleration of the ball, by using the following suvat equation:

where:
v = 0 is the final velocity of the baseball (it comes to rest)
u = 40 m/s is the initial velocity
a is the acceleration
s = 2.0 cm = 0.02 m is the displacement of the ball
Solving for a,

Now we can calculate the average force exerted on the ball, by using Newton's second law:

where
m = 300 g = 0.3 kg is the mass of the ball
is the acceleration
Substituting,

where the negative sign indicates that the direction of the force is opposite to the direction of motion of the ball.
Learn more about forces:
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Vehicle Kinematics: a
vehicle sliding sideways into a gravel pit, a vehicle
driving down a bank, a vehicle driving up a ramp and
a vehicle sliding laterally against a curb. "sliding
laterally against a curb" and "sliding sideways into a
gravel pit".
It would need to be over 20 because if the load of the Pulley E is 20 and the effort is 20, then they will be equal and the Pulley would not move, so your answer is at least 20