Answer:
The slower the train is moving, the less are the changes of the magnetic flux, thus the eddy currents become weaker.
Explanation:
A magnetic brakes is not a very efficient way of braking when a train is moving slowly because at low speeds, the changes in the magnetic flux are very less and so it causes the eddy current to become weaker.
Let us find the drag force which is proportional to the velocity of two conducting plates.
The EMF that is induced in the eddy currents are : 
The force which is due to the induced magnetic field is, 
Therefore, 

Here, force is directly proportional to the velocity of the two conducting plates.
Therefore, we can say that when the speed of the train is low, the magnetic flux changes are less and thus the eddy currents are weaker.
D. Humid Subtropical which is like hot subtype locate in climate zone with a 45 degree north to 50 degrees north which mostly in the east to 100th meridian
Oil, grease and dry lubricants
It is important to have the international system of units 'cause <span>it can be used by scientists everywhere around the world, and they will be able to understand each other with more accuracy.
In short, Your Answer would be Option D
Hope this helps!</span>