A-level · Forces & Newton's laws

Force diagrams, resultant force & equilibriumExam-style questions

What each force on a free-body diagram is and which way it points (weight always vertically down, normal reaction perpendicular to the surface, tension pulling along a string), why forces add as vectors so a resultant is found component-by-component, and what "in equilibrium" means — the resultant is zero, so the components balance.

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7 questions · A-level level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 2 Level 3 Level 4

1
A sack $S$ of weight $150$ N rests on rough horizontal ground. A light rope is attached to $S$ and is pulled with a force of magnitude $50$ N. The rope is inclined at an angle $\theta$ above the horizontal (see diagram).(a) Copy the diagram and add all the other forces acting on $S$ .

(1 mark)

$S$ does not move. The coefficient of friction between $S$ and the ground is $0.25$ .
(b) Show that $4\cos\theta + \sin\theta \le 3$ .

(5 marks)
Level 4 · 6 marksTry it