Question 1

What is the difference between mass and weight in physics?

Accepted Answer

Mass is the amount of matter in an object, measured in kilograms (kg), and it does not change with location. Weight is the force exerted on an object due to gravity, measured in newtons (N), and it depends on the gravitational field strength. For example, on Earth, a 10 kg mass has a weight of 98 N (using g = 9.8 N/kg), but on the Moon, the same mass would weigh only about 16 N because gravity is weaker.

Question 2

How do you calculate resultant force when forces are at an angle?

Accepted Answer

When forces act at an angle, you cannot simply add them arithmetically because they are vectors. Use a scale drawing (vector diagram) or resolve them into perpendicular components. For example, if two forces of 3 N and 4 N act at right angles, the resultant is 5 N (using Pythagoras: √(3²+4²) = 5). For non-right angles, use the parallelogram method or trigonometry (cosine rule).

Question 3

What is the elastic limit and why is it important?

Accepted Answer

The elastic limit is the maximum force a material can withstand and still return to its original shape when the force is removed. Beyond this point, the material becomes permanently deformed (plastic deformation). In Hooke's Law experiments, it's important to stay below the elastic limit to ensure the spring obeys the law (force ∝ extension). Exceeding it can damage the spring and invalidate results.

Question 4

How do Newton's laws apply to a car crash?

Accepted Answer

In a car crash, Newton's First Law explains why passengers continue moving forward at the car's original speed until a force (e.g., from a seatbelt or airbag) stops them. Newton's Second Law (F = ma) shows that a large deceleration (negative acceleration) produces a large force, which can cause injury. Seatbelts and airbags increase the stopping distance, reducing deceleration and thus the force on the passenger. Newton's Third Law: the car exerts a force on the wall, and the wall exerts an equal force back on the car, causing damage.

Question 5

What is the difference between a scalar and a vector quantity?

Accepted Answer

A scalar quantity has only magnitude (size), such as speed, mass, or temperature. A vector quantity has both magnitude and direction, such as velocity, force, or acceleration. For example, 5 m/s is a scalar (speed), but 5 m/s north is a vector (velocity). When adding vectors, you must consider direction; scalars can be added normally.

Question 6

How do you find the spring constant from a force-extension graph?

Accepted Answer

The spring constant (k) is the gradient of the straight-line portion of a force-extension graph (where Hooke's Law applies). Choose two points on the line, calculate change in force divided by change in extension (k = ΔF/Δx). The units are N/m. For example, if a force of 10 N causes an extension of 0.2 m, k = 10/0.2 = 50 N/m. Ensure the line passes through the origin; if not, the spring may have initial tension.

Topic 9 – Forces and their effects

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 9 – Forces and their effects — Edexcel GCSE Physics

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