O Level Forces and Pressure Worked Examples for 2026/2027 (Singapore MOE Syllabus) — Step-by-Step Worked Examples

Quick answer

Ever felt that sinking feeling when a physics question looks nothing like what you've studied? You're not alone. Here, I'll walk you through four worked examples on forces and pressure, showing each step and why it matters. By the end, you'll feel more confident about tackling these questions in your exams.

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What you need to know

Forces and pressure are about understanding how objects interact and how that interaction affects them. A force can push or pull an object, while pressure is the force spread over a certain area.

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Core teaching sections

Understanding Forces

Forces are pushes or pulls that can change an object's motion. They can make things move, stop, or change direction. Simple as that! In physics, we measure force in newtons (N). Remember, forces are vectors, which means they have both magnitude (size) and direction.

Understanding Pressure

Pressure is the amount of force applied over a specific area. Imagine standing on a beach, your feet sink into the sand, right? Now, lie down flat — you sink less. That's because your weight (force) is spread over a larger area, reducing pressure.

Common mistakes students make

1. Mixing up force and pressure: Many students confuse these terms. Remember, force is a push or pull, while pressure is force on a surface area.

2. Ignoring units: Always check the units, especially when converting between different measurements. Marks are lost here!

3. Forgetting direction in force questions: Forces have direction. If you miss this, your answer might be incomplete.

Exam tip

Precision beats length every time. Instead of writing long answers, focus on giving specific details. For forces questions, always include direction and magnitude.

Worked examples

Question 1: Calculating Force

A hawker centre table weighs 30 kg. What is the force of gravity acting on it?

Solution

Step 1: Identify the mass.

• Mass of the table is 30 kg.

Step 2: Use the formula for gravitational force: $𝐹 = 𝑚 \times 𝑔$, where $𝑔 = 9.8 \text{ m/s}^2$.
Why: To find the force, you need to multiply the mass by gravitational acceleration.

Step 3: Calculate the force: $𝐹 = 30 \times 9.8 = 294 \text{ N}$.
Why: This gives you the force in newtons, which is the standard unit of force.

Question 2: Calculating Pressure

A box with a weight of 500 N is placed on the ground. The box's base area is 2 m². Find the pressure exerted by the box.

Solution

Step 1: Identify the force and area.

• Force = 500 N, Area = 2 m².

Step 2: Use the pressure formula: $𝑃 = \frac{𝐹}{𝐴}$.
Why: Pressure is calculated by dividing force by area.

Step 3: Calculate the pressure: $𝑃 = \frac{500}{2} = 250 \text{ N/m}^2$.
Why: This shows how much force is applied per square meter.

Question 3: Net Force and Direction

A student pushes a trolley with 10 N to the right, while another student pushes it with 4 N to the left. What is the net force?

Solution

Step 1: Identify the forces and their directions.

• Right: 10 N, Left: 4 N.

Step 2: Subtract the smaller force from the larger force: $10 - 4 = 6 \text{ N}$.
Why: This gives you the magnitude of the net force.

Step 3: Determine the direction: The net force is 6 N to the right.
Why: Since the larger force is to the right, the net force follows that direction.

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Question 4: Pressure with Different Areas

A man weighing 800 N stands on a plank that's 0.5 m². If he lies down and spreads his weight over 2 m², what happens to the pressure?

Solution

Step 1: Calculate the initial pressure: $𝑃_1 = \frac{800}{0.5} = 1600 \text{ N/m}^2$.
Why: This is the pressure when standing.

Step 2: Calculate the pressure when lying down: $𝑃_2 = \frac{800}{2} = 400 \text{ N/m}^2$.
Why: Spreading the force over a larger area decreases the pressure.

Step 3: Compare the pressures.

• Standing: 1600 N/m², Lying down: 400 N/m².
  Why: The pressure decreases because the force is spread over a larger area.

Quick summary

• Force: Push or pull, measured in newtons (N).
• Pressure: Force per area, measured in N/m².
• Gravitational force formula: $𝐹 = 𝑚 \times 𝑔$.
• Pressure formula: $𝑃 = \frac{𝐹}{𝐴}$.
• Net force considers both magnitude and direction.
• Precision and correct units save marks!

FAQ

Q: What is the difference between force and pressure?
Force is a push or pull on an object, while pressure is the force distributed over an area.

Q: How do I calculate gravitational force?
Use the formula $𝐹 = 𝑚 \times 𝑔$, where 𝑚 is mass and 𝑔 is gravitational acceleration (9.8 m/s²).

Q: Why is direction important in force questions?
Direction helps determine the net force, which affects how objects move.

Q: What units should I use for force and pressure?
Force is measured in newtons (N) and pressure in newtons per square meter (N/m²).

Practise with free question sets

Work through more exam-style questions with answers and step-by-step solutions:

• 35+ O Level Forces and pressure Practice Questions for 2026 (based on Singapore MOE Syllabus)
• Topic study hub

Want unlimited similar questions with AI marking? Practise on Tutorly.sg/app

Related Topics You Should Learn Next

• O Level Physics: Understanding Forces and Pressure Made Simple
• O Level Physics Forces and Pressure: Complete Guide for Singapore Students
• How To Solve Questions Under Pressure For Singapore Secondary & O Level Students
• How to Score Full Marks in PSLE Science Forces Questions

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