From the formula F = (Gm1m2)/r2, if F = 100N, m1 = 5.0Kg and r = 2m, find G.

$$G = \frac{F r^2}{M m}$$

The formula with $G$ as the subject is $\boxed{G = \frac{F r^2}{M m}}$.

2.

$F = 100 \, \text{N}$, $M = 5.0 \, \text{kg}$, $m = 3.0 \, \text{kg}$, and $r = 2 \, \text{m}$.

$$G = \frac{(100 \, \text{N}) (2 \, \text{m})^2}{(5.0 \, \text{kg}) (3.0 \, \text{kg})}$$

$$G = \frac{400 \, \text{N} \cdot \text{m}^2}{15 \, \text{kg}^2}$$ $$G \approx 26.67 \, \text{N} \cdot \text{m}^2/\text{kg}^2$$

The value of $G$ is $\boxed{26.67 \, \text{N} \cdot \text{m}^2/\text{kg}^2}$.

3.
Gravitational potential is the work done per unit mass to move a test mass from infinity to a point in a gravitational field. It is always negative and is associated with mass.
Electric potential is the work done per unit charge to move a test positive charge from infinity to a point in an electric field. It can be positive or negative and is associated with electric charge.

4.
Two processes of demagnetisation are:

• Heating: When a magnetic material is heated above its Curie temperature, the increased thermal energy causes the magnetic domains to lose their alignment, resulting in demagnetisation.
• Hammering/Mechanical Shock: Repeatedly striking a magnet or subjecting it to strong mechanical vibrations can disorient the magnetic domains, causing them to become randomly arranged and thus demagnetising the material.