Edexcel IGCSE Physics 1.17 Force Mass and Acceleration Questions

Find the net force first when forces act together, then apply F = ma with consistent mass units and direction signs.

Exam points

State, rearrange and use the unbalanced-force equation F = ma to calculate force, mass or acceleration.
Combine forces to find the resultant before calculating acceleration and its direction.
Convert mass units and use consistent signs when applying F = ma in motion contexts.

[Maximum number: 5]

Diagram 1 shows some apparatus used to demonstrate the magnetic force on a current-carrying wire in a magnetic field.

Diagram 1

The wire has a mass of 6.5 g .

There is an upwards magnetic force of 34 mN acting on the wire.

Calculate the acceleration of the wire.
acceleration = $\mathrm{m} / \mathrm{s}^{2}$

Marking points:
- resultant force is the difference between weight and magnetic force
- resultant force = $31\ \mathrm{mN}$
- substitution into F=ma
- rearrangement
- evaluation

Example:
$F_{\mathrm{resultant}}=65-34=31\ \mathrm{mN}$ $31\times10^{-3}=6.5\times10^{-3}a$ $a=\frac{31\times10^{-3}}{6.5\times10^{-3}}=4.8\ \mathrm{m}\,\mathrm{s}^{-2}$
Allow ECF from (b)(i). Accept $4.57\ \mathrm{m}\,\mathrm{s}^{-2}$ when $g=9.81\ \mathrm{m}\,\mathrm{s}^{-2}$ is used.
POT error gives a 1 mark penalty.
5.2(3) scores 3 MAX when there is no evidence of the resultant-force idea.

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Edexcel IGCSE Physics 1.17 Force Mass and Acceleration Questions question 1