Forces, Movement, Shape, and Momentum
5 marks · NormalA cyclist of mass 75 kg is travelling along a road. A 12 N friction force opposes their motion. The cyclist pedals, applying a driving force of 22 N forward.
State the size and direction of the resultant force.
Calculate the acceleration of the cyclist.
Explain what will happen to the cyclist if the driving force is reduced to 12 N.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 10 N, forward N
(b) 0.13 m/s²
(c) There will be no unbalanced force; the cyclist will move at constant velocity because the driving force equals the friction force.
Common mistakes: Subtracting incorrectly or wrong direction; Using wrong mass
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct subtraction with correct direction stated.
M2 (b) · 1 mark · Uses F = ma and substitutes correctly. (follow-through)
A1 (b) · 1 mark · Correct answer (0.13 m/s²). (follow-through)
E1 (c) · 1 mark · States what happens if forces are balanced.
A2 (c) · 1 mark · Correctly relates balanced forces to constant velocity.
Worked solution
a) Resultant force = Driving force − friction = 22 N − 12 N = 10 N, forward
b) F = ma ⇒ a = F / m = 10 / 75 = 0.13 m/s²
c) If the driving force is reduced to 12 N, friction and driving force are equal and opposite. No resultant force acts, so the cyclist will move at constant velocity (no acceleration).