b) i) State the principle of moments. ii) Determine the value of X, assuming that the beam is balanced. iii) Calculate the reaction force acting at the pivot, given that the beam is balanced.

$$
X \times 3 \text{ m} = 90 \text{ Nm}
$$
$$
X = \frac{90 \text{ Nm}}{3 \text{ m}}
$$
$$
X = 30 \text{ N}
$$
The value of X is $\boxed{\text{30 N}}$.

• iii) Calculate the reaction force acting at the pivot, given that the beam is balanced. Assumption: Only the labeled forces (30 N and X N) contribute to the downward forces. The weight of the beam acts at the pivot and thus does not contribute to the net vertical force for equilibrium calculation, and the block's weight is negligible.

$$
R = 30 \text{ N} + 30 \text{ N}
$$
$$
R = 60 \text{ N}
$$
The reaction force acting at the pivot is $\boxed{\text{60 N}}$.

2.c) State one difference between mass and weight.

• Mass is a measure of the amount of matter in an object, while weight is the gravitational force acting on an object. Mass is constant regardless of location, whereas weight varies depending on the gravitational field strength.

3.a)

• i) Explain what happens if a device that draws 8A is used. If a device that draws $8 \text{ A}$ is used with a fuse rated at $5 \text{ A}$, the current will exceed the fuse's rating. The fuse wire will melt due to the excessive heat generated by the high current, breaking the circuit and protecting the device and wiring from damage.

• ii) Why are household circuits wired in parallel instead of series? Household circuits are wired in parallel so that each appliance receives the full supply voltage, allowing them to operate at their intended power. Additionally, if one appliance fails or is switched off, the other appliances in the circuit can continue to function independently.

3.b)

• i) Consider when the key, K, is open. What will be the ammeter reading? When the key K is open, the circuit is incomplete, meaning no current can flow through it.