To solve this problem we will apply the concepts related to the Doppler effect. The Doppler effect is the change in the perceived frequency of any wave movement when the emitter, or focus of waves, and the receiver, or observer, move relative to each other. Mathematically it can be described as,

Here,
= Frequency of Source
= Speed of sound
f = Frequency heard before slowing down
f' = Frequency heard after slowing down
v = Speed of the train before slowing down
So if the speed of the train after slowing down will be v/2, we can do a system equation of 2x2 at the two moments, then,
The first equation is,



Now the second expression will be,



Dividing the two expression we have,

Solving for v, we have,

Therefore the speed of the train before and after slowing down is 22.12m/s
Answer:

Explanation:
Given that,
The mass of a Hubble Space Telescope, 
It orbits the Earth at an altitude of 
We need to find the potential energy the telescope at this location. The formula for potential energy is given by :

Where
is the mass of Earth
Put all the values,

So, the potential energy of the telescope is
.
Here when car in front of us applied brakes then it is slowing down due to frictional force on it
So here we can say that friction force on the car front of our car is given as

So the acceleration of car due to friction is given as



now it is given that


so here we have


so the car will accelerate due to brakes by a = - 8.52 m/s^2
Answer:
current I1 = current I2
Explanation:
since the wire is made up of the same material, from Kirchoff's current law sum of currents entering a particular node or segment of wire is equals to the sum of currents leaving that particular node or segment of wire
Hydrogen has one proton whereas helium has two protons in its nucleus.
<h3>How hydrogen and helium atoms different from one another?</h3>
Atoms of hydrogen have a single proton in their nucleus and a single electron in the lowest energy level while on the other hand, Helium atoms have two protons in the nucleus and two electrons in the lowest energy level. In this way, we can say that the atomic number of hydrogen is 1 whereas the atomic number of helium is 2 because of the presence of two protons. Hydrogen atom has no neutron while on the other hand, the helium atom has one neutron in its nucleus.
So we can conclude that Hydrogen has one proton whereas helium has two protons in its nucleus.
Learn more about atom here: brainly.com/question/6258301
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