No light does not need medium to travel.Its an electromagnetic(EM) wave.All EM waves travel independent of medium. In contrast mechanical waves need a medium,sound waves,shock waves are mechanical and they need medium to transfer energy or travel.
the mass number minus the atomic number
The resistance of the sample is 
Explanation:
The relationship between resistance of a material and temperature is given by the equation

where
is the resistance at the temperature 
is the temperature coefficient of resistance
For the sample of nickel in this problem, we have:
when the temperature is 
While the temperature coefficient of resistance of nickel is

Therefore, the resistance of the sample when its temperature is

is

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Answer: A force must cause a displacement in order for work to be done. A book falls off a table and free falls to the ground. Yes. This is an example of work.
Explanation: