The Doppler effect is the right concept to solve this problem. The Doppler effect is understood as the change in apparent frequency of a wave produced by the relative movement of the source with respect to its observer. Mathematically it can be described as,

Here,
= Frequency of the sound from the Whistle
f = Frequency of sound heard
v = Speed of the sound in the Air
Replacing we have that





Therefore the minimum speed to know if the whistle is working is 16.33m/s
<u><em>The question doesn't provide enough data to be solved, but I'm assuming some magnitudes to help you to solve your own problem</em></u>
Answer:
<em>The maximum height is 0.10 meters</em>
Explanation:
<u>Energy Transformation</u>
It's referred to as the change of one energy from one form to another or others. If we compress a spring and then release it with an object being launched on top of it, all the spring (elastic) potential energy is transformed into kinetic and gravitational energies. When the object stops in the air, all the initial energy is now gravitational potential energy.
If a spring of constant K is compressed a distance x, its potential energy is

When the launched object (mass m) reaches its max height h, all that energy is now gravitational, which is computed as

We have then,


Solving for h

We have little data to work on the problem, so we'll assume some values to answer the question and help to solve the problem at hand
Let's say: x=0.2 m (given), K=100 N/m, m=2 kg
Computing the maximum height


The maximum height is 0.10 meters
Given that,
Mass of each washer = 4.9 g
We need to calculate the mass of two washers in kg
Using conversion of unit
Mass of each washer 
So, Mass of two washers is

Put the value of m


If 4 washer are attached to the spring
We need to calculate the applied force on the car
Using formula of force

Put the value into the formula


Hence, (i), The mass of two washers is 0.0098 kg.
(ii). The applied force on the car is 0.192 N.
Herz is a measurement for how many cycles of the wave occur per second, which in this case is 261. the period is the time it takes to complete 1 cycle, so if 261 cycles occur per second, one cycle occurs every 1/261 seconds
The question to the above information is;
What is the best use of an atomic model to explain the charge of the particles in Thomson's beams?
Answer;
An atom's smaller negative particles are at a distance from the central positive particles, so the negative particles are easier to remove.
Explanation;
-Atoms are comprised of a nucleus consisting of protons (red) and neutrons (blue). The number of orbiting electrons is the same as the number of protons and is termed the "atomic number" of the element.
J.J. Thomson discovered the electron. Atoms are neutral overall, therefore in Thomson’s ‘plum pudding model’:
- atoms are spheres of positive charge
- electrons are dotted around inside