The two different isotopes have weights :
w1 = 78.918 amu
w2 = 80.916 amu
average weight w3 = 79.903 amu
The mixing of two components can be modeled as
let the fraction of w1 be 'x'
hence 
now this is a linear equation in 'x'. Substituting the values we get
x = 0.507
hence the percentage of Br79 = 50.7% and the percentage of BR81 = 49.3%
Answer:
The Universe became transparent to the light left over from the Big Bang when it was roughly 380,000 years old
Explanation:
Answer:
The magnitude of the electric field at a point equidistant from the lines is 
Explanation:
Given that,
Positive charge = 24.00 μC/m
Distance = 4.10 m
We need to calculate the angle
Using formula of angle



We need to calculate the magnitude of the electric field at a point equidistant from the lines
Using formula of electric field

Put the value into the formula



Hence, The magnitude of the electric field at a point equidistant from the lines is 
Answer:
Second one
Explanation:
Lying on the floor is something you can do with the least amount of energy
The tension in the string with friction would be the biggest because of the involvement of the force of gravity. This would result in that the friction force that is acting on the system. There is no friction in the frictionless system, and only the force of gravity is relevant.