Physics — Question 5
QCAA 2025, Paper 2 · 5 marks
Q5 · 2025 · Paper 2Complex familiar5 marks
QUESTION 5 (5 marks)
Three point charges, A, B and C, are set up as shown.
Determine the net force acting on charge B. Show your working.
WORKED SOLUTION
QCAA guide · typeset solution
5 marksANSWERSee worked solution below.
Worked solution
F=r2kQq
FA on B=0.0602(9×109)(−4.2×10−6)(8.4×10−6)=−88.2
=88.2N attraction FC on B=0.1402(9×109)(2.1×10−6)(8.4×10−6)=8.1
=8.1N repulsion Fresultant=88.22+8.12=88.57
Magnitude of net force = 89N tanθ=88.28.1
θ=N 5.2∘ W Direction of net force = N 5.2∘ W recognises that the scenario relates to the force between two charges
calculates magnitude of force between A and B
calculates magnitude of force between B and C
determines magnitude of net force
determines direction of net force
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
How many marks did you earn?Compare your working with the guide above.