Friction between two surfaces can cause resistance to motion. Outline THREE applications of friction.

The force exerted is the man's weight.

$$F = m \times g$$ $$F = 80 \text{ kg} \times 10 \text{ N/kg}$$ $$F = 800 \text{ N}$$

The problem states the area is $420 \text{ m}^2$. However, this value would result in an extremely low pressure. Given the context of a shoe and the student's implied calculation, it is highly probable that the area was intended to be $420 \text{ cm}^2$. We will proceed with this assumption for a realistic answer.

$$A = 420 \text{ cm}^2 = 420 \times (10^{-2} \text{ m})^2 = 420 \times 10^{-4} \text{ m}^2$$ $$A = 0.042 \text{ m}^2$$

Pressure is defined as force per unit area.

$$P = \frac{F}{A}$$ $$P = \frac{800 \text{ N}}{0.042 \text{ m}^2}$$ $$P \approx 19047.62 \text{ N/m}^2$$ $$P \approx 19047.62 \text{ Pa}$$

The average pressure exerted on the floor is $\boxed{\text{19047.62 Pa}}$

4. Heat is a form of energy that can be transferred from one place to another by virtue of temperature difference. List THREE modes of heat transfer. (3 Marks)

• Conduction
• Convection
• Radiation

5. In the workshops different machines are used for different purposes. Define a simple machine (2 Marks)
A simple machine is a device which enables a small force (otherwise known as the effort), acting at a point to overcome large force (called load) acting at some other point.

6. Calculate the work done when a mass is lifted vertically by a crane to a height of $5 \text{ m}$, the force required to lift the mass being $98 \text{ N}$. (3 Marks)

Work done is calculated as the product of force and distance in the direction of the force.

$$W = F \times d$$

$$W = 98 \text{ N} \times 5 \text{ m}$$ $$W = 490 \text{ J}$$

The work done is $\boxed{\text{490 J}}$

7. Machines make work easier and saves time. State five examples of simple machines. (5 Marks)

• Lever
• Pulley
• Wheel and Axle
• Inclined Plane
• Wedge