Answer:
Explanation:
We have the following relation between power, P and intensity, I

= 
= 
We also have the following relationship between electric field and electromagnetic radiation thus

Hence 
substituting the values of I, c and e, we have

Lets make the original number of nuclides at the start is 100.
If 7/8 of 100 is decayed, that means 87.5 decayed.

And there is 1/8 left of the number of nuclide 100. Which is 12.5


How many Half lifes passed for 100 to become 12.5 is 3 Half-Lives.

Each Half-Life is 80 seconds so there is 240 seconds

The answer is that it takes 240 seconds.
Given: Mass m = 60 Kg
Weight W = 96 N
Required: Acceleration due to gravity, g = ?
Formula: W = mg
g = W/g
g = 96 Kg.m/s²/60 Kg (note: this is the derive unit for Newton "N")
g = 1.6 m/s²
Answer:
U = 1 / r²
Explanation:
In this exercise they do not ask for potential energy giving the expression of force, since these two quantities are related
F = - dU / dr
this derivative is a gradient, that is, a directional derivative, so we must have
dU = - F. dr
the esxresion for strength is
F = B / r³
let's replace
∫ dU = - ∫ B / r³ dr
in this case the force and the displacement are parallel, therefore the scalar product is reduced to the algebraic product
let's evaluate the integrals
U - Uo = -B (- / 2r² + 1 / 2r₀²)
To complete the calculation we must fix the energy at a point, in general the most common choice is to make the potential energy zero (Uo = 0) for when the distance is infinite (r = ∞)
U = B / 2r²
we substitute the value of B = 2
U = 1 / r²