DP Physics (first assessment 2025)

Question EXE.2.HL.TZ0.7

Date	Example questions Example questions	Marks available	[Maximum mark: 6]	Reference code	EXE.2.HL.TZ0.7
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate, Determine, State	Question number	7	Adapted from	N/A

[Maximum mark: 6]

EXE.2.HL.TZ0.7

A flywheel of radius $R = 0.15 m$ and mass $M = 1.8 kg$ rotates around the central axis. The moment of inertia of the flywheel is $\frac{1}{2} M R^{2}$ . A thread is wrapped around the flywheel and a time-varying force $F$ is applied to the thread.

The angular velocity of the flywheel increases from 4.0 rad s⁻¹ to 9.0 rad s⁻¹ in a time of 0.24 s.

(a)

Calculate the angular impulse delivered to the flywheel during the acceleration.

[2]

Markscheme

$Δ L = l Δ ω = \frac{1}{2} \times 1.8 \times 0 . 15^{2} (9.0 - 4.0)$ ✓

$0.10$ «N m s» ✓

(b)

Determine the average magnitude of $F$ .

[2]

Markscheme

Average torque $= \frac{Δ L}{Δ t} = \frac{0.10}{0.24} = 0.42$ «N m» ✓

Average force $= \frac{τ}{R} = \frac{0.42}{0.15} = 2.8$ «N» ✓

(c)

State two assumptions of your calculation in part (b).

[2]

Markscheme

No other forces than F provide the torque ✓

The thread unwinds without slipping ✓

The thread is weightless ✓

F is always tangent to the flywheel ✓

Syllabus sections

A. Space, time and motion

A. Space, time and motion » A.4 Rigid body mechanics

Question EXE.2.HL.TZ0.7

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