Answer:
1.5 × J
Explanation:
The initial force, which in this case is the external force is equal to 15N. Logically, when 150 Joules of work is done upon that system the overall energy will increase by that very same amount of work applied on the system which is 150 J.
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