IB Physics HL A 2 4 Resultant Force From Diagrams Questions

Practise analysing HL equilibrium systems with coplanar forces, tension, circular paths, slopes and coupled bodies.

Exam points

Resolve forces into components or combine force vectors from a diagram to determine the magnitude and direction of the resultant.
Test whether the vector sum is zero and use that result to identify translational equilibrium, including coplanar three-force systems.
Use force geometry and equilibrium equations to determine an unknown tension, component or contact force on slopes, ladders and suspended charged bodies.
Interpret a non-zero resultant in curved or constrained motion, including identifying the force direction required for circular motion.
Distinguish a zero resultant from zero individual forces and explain what the resultant implies about acceleration or constant velocity.

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Study A.2.4—Resultant force from diagrams conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 3]

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.

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The thread makes an angle of $30^{\circ}$ with the vertical wall. The ball has a mass of 0.025 kg .

Determine the horizontal force that acts on the ball.

Horizontal force on ball: $F = T\sin 30$ .
$T = \frac{mg}{\cos 30}$ .
$F = mg\tan 30 = 0.025 \times 9.8 \times \tan 30 = 0.14\ \text{N}$ .

Allow $g=10\ \text{N kg}^{-1}$ .
Award [3] marks for a bald correct answer.
Award [1 max] for an answer of zero if the horizontal force is interpreted as the horizontal component of the net force.

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IB Physics HL A 2 4 Resultant Force From Diagrams Questions question 1