Forces, Motion and Elasticity

IGCSE Edexcel Physics
1.11–1.24 Forces, Resultant Force, Stopping Distance, Elasticity
Key Concepts: Forces can change speed, direction and shape. Resultant force determines acceleration. Friction opposes motion. Extension is proportional to force in the linear region (Hooke's law).

Section A: Forces and Resultant Force

1. State three effects of forces and give one example for each. [3]
2. Identify gravitational and electrostatic forces in everyday examples and state one scalar and one vector quantity. [3]
3. Calculate the resultant force on a car if 900 N acts forward and 250 N acts backward. [2]
4. A 12 kg box accelerates at 1.5 m/s². Calculate the resultant force. [2]

Section B: Weight, Friction and Stopping Distance

5. Calculate the weight of a 60 kg person on Earth ($g = 9.8\,N/kg$). [2]
6. Define friction and give two factors that increase stopping distance. [3]
6a. State the relationship between thinking distance, braking distance and stopping distance. [2]

Section C: Terminal Velocity

7. Explain how terminal velocity is reached for a falling object. [3]

Section D: Elasticity and Hooke's Law

8. Describe a practical to investigate how extension varies with applied force for a spring. Include one variable to control and the graph you would plot. [4]
9. A spring extends 4 cm when a force of 2 N is applied. What extension occurs at 5 N (within linear region)? [2]
10. Describe elastic behaviour and state what Hooke's law means on a force-extension graph. [3]

Total marks: 29

Mark Scheme

1. Speed, direction, shape (with examples) [3]
2. Examples: gravity (falling object) and electrostatic (charged balloon); scalar e.g. speed, vector e.g. force/velocity [3]
3. 650 N forward [2]
4. $F = ma = 12 \times 1.5 = 18\,N$ [2]
5. $W = mg = 60 \times 9.8 = 588\,N$ [2]
6. Friction opposes motion; factors: speed, mass, road condition, reaction time (any two) [3]
6a. Stopping distance = thinking distance + braking distance [2]
7. Air resistance increases with speed; when it equals weight, resultant force is zero and speed is constant [3]
8. Measure extension for a range of forces; keep spring the same; plot force vs extension and look for linear region [4]
9. Proportional: $2\,N -> 4\,cm$, $5\,N -> 10\,cm$ [2]
10. Elastic returns to original shape; linear region means extension proportional to force [3]