The questions are on the resultant force test. Take it under real conditions before reading the mark scheme.
Quick answer: A resultant force is the single force that has the same effect as all the forces acting on an object. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 9-10 test on resultant force, from resultant force to non-contact forces, with the equivalent answers to accept.
Marks are shown for each part. Method marks are given when your working is clear, even if the final answer is wrong, so state the rule you use and always give a direction for forces.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P5
Question 1 Resultant force (2 marks)
- The single force that has the same effect as all the forces acting on the object together.
- It stays at rest or moves at constant velocity.
Marking: 1 mark each.
Question 2 Weight and reaction (3 marks)
- W = m g = 3.5 × 9.8 = 34.3 N.
- The bag is at rest, so the reaction is 34.3 N upwards.
Marking: (a) 1 mark equation, 1 mark value; (b) 1 mark.
Question 3 Forces on a line (3 marks)
- 8.0 − 5.0 = 3.0 N to the right.
- The resultant becomes 8.0 N to the right.
Marking: (a) 1 mark subtraction, 1 mark direction; (b) 1 mark.
Question 4 Reading a free-body diagram (3 marks)
- 40 − 15 = 25 N to the right.
- 49 − 49 = 0 N.
- The crate accelerates to the right.
Marking: 1 mark each part.
Question 5 Perpendicular forces (3 marks)
R² = 9.0² + 12² = 81 + 144 = 225, so R = 15 N. tan θ = 12 ÷ 9.0 = 1.33, so θ = 53° north of east.
Marking: 1 mark for Pythagoras, 1 mark for 15 N, 1 mark for the angle.
Question 6 Constant speed (2 marks)
The velocity is constant, so the resultant force is zero. The driving force equals the resistive forces (friction and drag) in the opposite direction.
Marking: 1 mark for resultant zero, 1 mark for the balance of driving and resistive forces.
Question 7 Hanging lamp (2 marks)
W = m g = 2.0 × 9.8 = 19.6 N. The lamp is at rest, so the tension equals the weight: 19.6 N (about 20 N).
Marking: 1 mark for the weight, 1 mark for tension equal to weight.
Question 8 Non-contact forces (2 marks)
Any two of: gravity (a ball falling), magnetic force (a fridge magnet pulling a pin), electrostatic force (a charged comb lifting paper).
Marking: 1 mark for each force with a correct example.
