DP Physics (first assessment 2025)

Question EXE.2.HL.TZ0.8

Date	Example questions Example questions	Marks available	[Maximum mark: 7]	Reference code	EXE.2.HL.TZ0.8
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate, Compare	Question number	8	Adapted from	N/A

[Maximum mark: 7]

EXE.2.HL.TZ0.8

A ring of mass M = 0.32 kg and radius R = 0.25 m is accelerated from rest by a constant torque of 0.20 N m. The moment of inertia of the ring is MR².

(a)

Calculate:

(a.i)

the angular acceleration of the ring;

[2]

Markscheme

$α = \frac{τ}{l} = \frac{0.20}{0.32 \times 0 . 25^{2}}$ ✓

$10$ «rad s⁻²» ✓

(a.ii)

the angular velocity of the ring after a time of 5.0 s.

[1]

Markscheme

$10 \times 5.0 = 50$ «rad s⁻¹» ✓

(b)

A solid disc of the same mass and radius as the ring is accelerated by the same torque. Compare, without calculation:

(b.i)

the angular impulse delivered to the disc and to the ring during the first 5.0 s.

[2]

Markscheme

The angular impulse is the product of torque and time ✓

Both factors are the same so the angular impulse is the same ✓

(b.ii)

the final kinetic energy of the disc and the ring.

[2]

Markscheme

The disc has a smaller moment of inertia «because its mass is distributed closer to the axis of rotation» ✓

From $E_{k} = \frac{L^{2}}{2 l}$ , the disc will achieve a greater kinetic energy «because $L$ is the same for both» ✓

Syllabus sections