A.4 Rigid body mechanics questions for IB Physics

80 questions on Rigid body mechanics, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.

IB Physics
Part of A Space, time and motion
HL only

Questions by paper and level

Paper	Questions
Paper 1A	37
Paper 2	43
Every paper	80

Counted on 10 November 2026

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Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.

Question 1 · PHY-00079Paper 1A · 1 mark

A solid sphere is released from rest and rolls without slipping down a slope, descending through a vertical height $h$ . A small block is released from rest at the same height and slides down a frictionless slope. The moment of inertia of a solid sphere of mass $M$ and radius $R$ about its centre is $\frac{2}{5} M R^{2}$ . What is $\frac{speed of the sphere at the bottom}{speed of the block at the bottom}$ ?

A
$\frac{5}{7}$
B
$\sqrt{\frac{5}{7}}$
C
$1$
D
$\sqrt{\frac{7}{5}}$

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Question 2 · PHY-00321Paper 2 · 10 marks

A solid cylinder of mass $M$ and radius $R$ is released from rest at the top of a ramp and rolls down it without slipping. The top of the ramp is 0.80 m above the bottom. The moment of inertia of the cylinder about its axis is $\frac{1}{2} M R^{2}$ . In a separate trial, a block is released from the same point and slides down the ramp with negligible friction. Air resistance is negligible.

(a)
Calculate the speed of the block at the bottom of the ramp.
1 mark
(b)
Show that the total kinetic energy of the cylinder when its centre moves at speed $v$ is $\frac{3}{4} M v^{2}$ .
2 marks
(c)
Calculate the speed of the centre of the cylinder at the bottom of the ramp.
2 marks
(d)
State the fraction of the cylinder's kinetic energy that is rotational.
1 mark
(e)
A frictional force acts on the cylinder at its point of contact with the ramp. Explain why no mechanical energy is transferred to thermal energy by this force.
2 marks
(f)
A thin-walled hollow cylinder of the same mass and radius, with moment of inertia $M R^{2}$ , is released at the same time as the solid cylinder. Predict, with a reason, which cylinder reaches the bottom of the ramp first.
2 marks

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Question 3 · PHY-00080Paper 1A · 1 mark

A flywheel of moment of inertia $I$ rotates at angular speed $ω$ . It drives a generator, and after a time $t$ its angular speed has fallen to $\frac{ω}{2}$ . What is the mean power transferred from the flywheel during this time?

A
$\frac{I ω^{2}}{8 t}$
B
$\frac{I ω^{2}}{4 t}$
C
$\frac{3 I ω^{2}}{8 t}$
D
$\frac{3 I ω^{2}}{4 t}$

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Question 4 · PHY-00375Paper 2 · 7 marks

The drum of a washing machine has a radius of 0.24 m and many small holes in its curved wall. During the final spin, the drum rotates at 1200 revolutions per minute. Wet clothes are pressed against the inside of the wall.

(a)
Calculate the angular velocity of the drum.
1 mark
(b)
Calculate the centripetal acceleration of the clothes, as a multiple of $g$ .
2 marks
(c)
Explain why water leaves the clothes through the holes in the wall.
2 marks
(d)
When the spin ends, the drum and clothes slow down uniformly from 1200 revolutions per minute to rest in 25 s. Their total moment of inertia about the axis is 0.18 kg m $^{2}$ . Calculate the average braking torque.
2 marks

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Question 5 · PHY-00127Paper 1A · 1 mark

A cyclist tightens a wheel nut with a spanner. She pulls on the handle with a force of 40 N at a distance of 0.25 m from the centre of the nut. The force makes an angle of 30° with the handle. What is the magnitude of the torque on the nut?

A
$5.0 N m$
B
$8.7 N m$
C
$10 N m$
D
$160 N m$

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Question 6 · PHY-00379Paper 2 · 7 marks

A small spice jar rests on a horizontal rotating tray on a dining table, at a distance of 0.20 m from the axis of the tray. The tray is spun from rest with a constant angular acceleration of 8.0 rad s $^{- 2}$ . The coefficient of static friction between the jar and the tray is 0.30. Treat the jar as a particle.

(a)
Explain why the frictional force on the jar is not directed towards the axis while the tray speeds up.
2 marks
(b)
Calculate the tangential acceleration of the jar.
1 mark
(c)
Determine the angular velocity of the tray when the jar starts to slide.
3 marks
(d)
Calculate the time after the start at which the jar starts to slide.
1 mark

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