Question 1

A rectangular block with dimensions 0.2 m x 0.1 m rests on a table. If the block weighs 4 N, calculate the pressure exerted on the table.

Accepted Answer

**Formula:** Pressure = Force / Area
**Calculation:**
Area = 0.2 m * 0.1 m = 0.02 m²
Pressure = 4 N / 0.02 m² = 200 N/m² or 200 Pa
**Answer:** The pressure exerted on the table is 200 Pa. Pressure is force distributed over an area.

Question 2

A sharp knife cuts better than a blunt knife. Explain why, in terms of pressure.

Accepted Answer

Pressure is defined as force per unit area (P = F/A). A sharp knife has a much smaller surface area in contact with the object being cut compared to a blunt knife. Therefore, for the same applied force, the sharp knife exerts a much larger pressure. This greater pressure allows the sharp knife to more easily overcome the resistance of the material being cut.

Question 3

A rectangular block of wood weighing 20 N rests on a table. The block is 0.5 m long and 0.2 m wide. Calculate the pressure exerted on the table by the block.

Accepted Answer

Pressure = Force / Area
Force = 20 N
Area = length x width = 0.5 m x 0.2 m = 0.1 m²
Pressure = 20 N / 0.1 m² = 200 N/m² or 200 Pa

The pressure is calculated by dividing the force (weight of the block) by the area of contact between the block and the table.

Question 4

Explain why it is easier to cut something with a sharp knife than with a blunt knife, even if you apply the same force.

Accepted Answer

Pressure = Force / Area. A sharper knife has a smaller surface area in contact with the object being cut. Since pressure is inversely proportional to area, a smaller area means a greater pressure for the same applied force. This greater pressure allows the sharp knife to cut more easily.

Question 5

Describe how the pressure at a point in a liquid changes as the depth increases. Explain your answer.

Accepted Answer

The pressure increases with depth. This is because the weight of the liquid above that point increases, and pressure is force (weight) per unit area. Therefore, a greater weight of liquid above means a greater pressure at that point.

Question 6

A submarine is submerged at a depth of 50 m in seawater. The density of seawater is 1025 kg/m³. State two factors that affect the pressure on the submarine.

Accepted Answer

1. The depth of the submarine in the water
2. The density of the seawater

Question 7

Calculate the pressure at a depth of 15 meters in a freshwater lake. The density of freshwater is 1000 kg/m³ and the gravitational field strength is 9.8 N/kg.

Accepted Answer

Δp = ρgh
Δp = (1000 kg/m³)(9.8 N/kg)(15 m)
Δp = 147000 Pa
Therefore, the pressure is 147000 Pascals. This calculation uses the formula relating pressure difference to the density of the fluid, gravitational field strength and depth.

Question 8

Explain why the pressure increases as you go deeper into a liquid.

Accepted Answer

As depth increases, the weight of the liquid above the point in question also increases. This increased weight exerts a greater force per unit area, resulting in a higher pressure. The formula Δp = ρgh shows that pressure change (Δp) is directly proportional to depth (h), density (ρ), and gravitational field strength (g). Therefore, increased depth directly causes increased pressure.

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