Answer:
1.045 m from 120 kg
Explanation:
m1 = 120 kg
m2 = 420 kg
m = 51 kg
d = 3 m
Let m is placed at a distance y from 120 kg so that the net force on 51 kg is zero.
By use of the gravitational force
Force on m due to m1 is equal to the force on m due to m2.



3 - y = 1.87 y
3 = 2.87 y
y = 1.045 m
Thus, the net force on 51 kg is zero if it is placed at a distance of 1.045 m from 120 kg.
Answer:
r = 0.728 m
Explanation:
The intensity is defined as the ratio between the power per unit area
I = P / A
Where A is the area of the sphere where the wave is
A = 4π r²
In this exercise we are given the power of the P = 10.0 W micro waves, the safe intensity I₁ = 1.5 W / m²
A₁ = P / I₁
Calculate
A₁ = 10.0 / 1.5
A₁ = 6.6667 m²
Let's clear the radius of the sphere
r = √ A / 4π
r = √ (6.6667 / 4π)
r = 0.728 m