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

Here are the solutions to the questions:

1. Friction between two surfaces can cause resistance to motion. Outline THREE applications of friction (3 Marks) • Walking: Friction between the road surface and shoe enables us to walk. • Matchstick: Friction between the matchstick and the rough surface enables lighting of fire. • Vehicle travelling on the road: Vehicles could not move if there was no friction between the tyres and the road surface.

2. Force is a product of mass and acceleration. State the polygon law of forces (3 Marks) • The polygon of forces rule states that; "If four or more coplanar forces acting at a point are in equilibrium, they can be represented in magnitude and direction by the sides of a polygon taken in order."

3. A man of $80 \text{ kg}$ stands upright on the floor if the area of contact of his shoe and floor is $420 m^2$ determine the average pressure he exerts on the floor. (Take $g=10 N/kg^{-1}$) (4 Marks)

Step 1: Calculate the force exerted by the man. The force exerted is the man's weight. $F = m \times g$ $F = 80 kg \times 10 \text{ N/kg}$ $F = 800 \text{ N}$

Step 2: Convert the area to square meters. The problem states the area is $420 m^2$. 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 $420 cm^2$. We will proceed with this assumption for a realistic answer. $A = 420 cm^2 = 420 \times (10^{-2} m)^2 = 420 \times 10^{-4} m^2$ $A = 0.042 m^2$

Step 3: Calculate the pressure. Pressure is defined as force per unit area. $P = \frac{F}{A}$ $P = \frac{800 N}{0.042 m^2}$ $P \approx 19047.62 N/m^2$ $P \approx 19047.62 \text{ Pa}$

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

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)

Step 1: Identify the formula for work done. Work done is calculated as the product of force and distance in the direction of the force. $W = F \times d$

Step 2: Substitute the given values and calculate. $W = 98 N \times 5 \text{ m}$ $W = 490 \text{ J}$

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

7. Machines make work easier and saves time. State five examples of simple machines. (5 Marks) • Lever • Pulley • Wheel and Axle • Inclined Plane • Wedge