The answer to the blank above is 20. The speed limit given provided that you cannot see the tracks for 400 ft in both directions is always 20 mph. Basically, this 20 mph is decided based upon the traffic laws in order to avoid road casualties. Since it is "uncontrolled railroad crossing", the minimum speed should be implemented to slow down for the purpose of traffic calming measures. Other than this, the 20 mph is also applicable in narrowing roads as well as speed humps.
Answer:

Explanation:
The problem must be addressed through the concepts of electromotive force. By Faraday's law it is defined that

Where
Electromotive Force
N = Number of Loops
A = Area
B = Magnetic Field (chaging through the time)
From this equation and our values, we need to find the time, then we re-arrange the equation



Therefore the time required for the magnetic field to decrease to zero from its maximum value is 
Answer:D
Explanation:
Given
mass of A is twice the mass of B half the velocity of B
Suppose
and
be the average force exerted on A and B respectively
and According to Newton third law of motion Force on the body A is equal to Force on body B but opposite in direction as they are action and reaction force.
Thus
and option d is correct
Answer:
the difference between the two is that the candle forms an emission spectrum and the book an absorption spectrum.
the book it is observed in all directions so that its reflection has to be diffused
Explanation:
The ray of light emitted by a candle is the light generated by the temperature of the flame, which is made up of the emissions of a black body at this temperature plus the emissions of the chemical elements that make up the candle.
The Light reflected from the cover of a book is the same incident light spectrum minus the wavelengths that create transitions in the elements of the cover, these wavelengths will be seen as dark areas.
As a consequence of the above, the difference between the two is that the candle forms an emission spectrum and the book an absorption spectrum.
For the cover of the book form a specular reflection the incident rays are reflected in one direction and the rest would be dark, but in the book it is observed in all directions so that its reflection has to be diffused
Answer:
15.71 m/s
Explanation:
We are given;
Time; t = 0.2 s
Radius; r = 0.5 m
The circumference will give us the distance covered.
Formula for circumference is 2πr
Thus; Distance = 2πr = 2 × π × 0.5 = π
Linear speed = distance/time = π/0.2 = 15.71 m/s