A-level · Forces & Newton's laws

FrictionExam-style questions

Friction as a force opposing motion, with magnitude up to a maximum F ≤ μR (and F = μR at the point of slipping) — on rough horizontal surfaces and slopes, the angle of friction tanα = μ, and F = ma with friction included.

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

DifficultyAll Level 2 Level 3 Level 4 Level 5

1
A horizontal force of magnitude $18$ N pulls a particle $P$ , of mass $4$ kg, in a straight line across a rough horizontal plane.

Apart from this force, the only horizontal force on $P$ is friction, of magnitude $F$ newtons. Figure 1 shows these two forces.Figure 1 — not accurately drawn
(a) Find the magnitude of the normal reaction of the plane on $P$ .

(1 mark)

$P$ accelerates at $2.5\ \text{m s}^{-2}$ in the direction of the $18$ N force.
(b) Find the value of $F$ .

(2 marks)

The coefficient of friction between $P$ and the plane is $\mu$
(c) Find the value of $\mu$ , giving your answer to 2 significant figures.

(1 mark)
Level 2 · 4 marksTry it
2
A particle $P$ of mass $6$ kg is placed on a rough horizontal plane and stays at rest. Figure 1 shows $P$ on the plane.Figure 1 — not accurately drawn
(a) Find the magnitude of the normal reaction of the plane on $P$ .

(1 mark)

The coefficient of friction between $P$ and the plane is $0.45$

A horizontal force of magnitude $X$ newtons now acts on $P$ , and $P$ remains at rest in limiting equilibrium.
(b) Find the value of $X$ .

(2 marks)
Level 2 · 3 marksTry it
3
A block of mass $4$ kg rests on a rough horizontal surface with coefficient of friction $0.3$ . Find the least horizontal force needed to move it, to 3 s.f. ( $g = 9.8$ .)
Level 2 · 2 marksTry it
4
A block of mass $2$ kg rests on a rough horizontal surface with coefficient of friction $0.5$ . A horizontal force of $6$ N is applied.

Determine whether the block moves, and state the magnitude of the frictional force acting. (3 marks)
Level 2 · 3 marksTry it
5
The block of mass $4$ kg ( $\mu = 0.3$ ) on a rough horizontal surface is now pushed by a horizontal force of $20$ N. Find its acceleration, to 3 s.f. ( $g = 9.8$ .)
Level 3 · 2 marksTry it

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