Answer:
The coefficient is 0.90
Explanation:
Drawing a diagram makes thing easier, we will assume that the acceleration tends to zero because it start barely moving.

Electro waves in a vacuum air is deals with this and electricity when the air and the electricity it makes electro magnets.
Answer:
From the second law of motion:
F = ma
we are given that the force applied on the block is 20N and the block accelerates at an acceleration of 4 m/s/s
So, F= 20N and a = 4 m/s/s
Replacing the variables in the equation:
20 = 4* m
m = 20 / 4
m = 5 kg