DP Physics (last assessment 2024)

Question 21M.2.HL.TZ2.3b.i

Date	May 2021	Marks available	[Maximum mark: 3]	Reference code	21M.2.HL.TZ2.3b.i
Level	HL	Paper	2	Time zone	TZ2
Command term	Determine	Question number	b.i	Adapted from	N/A

b.i.

[Maximum mark: 3]

21M.2.HL.TZ2.3b.i

A vertical wall carries a uniform positive charge on its surface. This produces a uniform horizontal electric field perpendicular to the wall. A small, positively-charged ball is suspended in equilibrium from the vertical wall by a thread of negligible mass.

(b.i)

The thread makes an angle of 30° with the vertical wall. The ball has a mass of 0.025 kg.

Determine the horizontal force that acts on the ball.

[3]

Markscheme

horizontal force $F$ on ball $= T \sin 30$ ✓

$T = \frac{m g}{\cos 30}$ ✓

$F « = m g \tan 30 = 0.025 \times 9.8 \times \tan 30 » = 0.14 « N »$ ✓