AQA A-Level Physics Paper 1, June 2022: Question 5

✅ Correct Answer

Time = 3.5 s (Accept values that round to 3.49 s)

💡 Key Knowledge

• Angular speed equation: ω = θ / t or ω = 2π / T
• One complete revolution corresponds to an angle of 2π radians.

📐 Calculation Steps

1. Rearrange for time: t = θ / ω
2. Substitute values: t = 2π / 1.8
3. Evaluate: t = 3.4906... s (rounds to 3.5 s)

❌ Common Errors

Forgetting that one full circle is 2π radians rather than just π radians.

✅ Correct Answer

An arrow originating from the block pointing directly towards the centre of the turntable.

💡 Key Knowledge

Centripetal force is not a new type of force; it is the resultant force acting towards the centre of a circular path that causes centripetal acceleration.

🧠 Exam Technique

Ensure your arrow starts precisely on the block and points accurately along the radius towards the central pivot point.

✅ Correct Answer

0.097 N (Calculator value: 0.0972 N)

💡 Key Knowledge

Centripetal force formula: F = m ω² r or combining a = ω² r with F = ma .

📐 Calculation Steps

1. Identify variables: m = 0.12 kg , ω = 1.8 rad s⁻¹ , r = 0.25 m
2. Substitute into formula: F = 0.12 × (1.8)² × 0.25
3. Calculate: F = 0.12 × 3.24 × 0.25 = 0.0972 N

❌ Common Errors

Failing to square the angular speed ( ω ) or using diameter instead of radius ( r = 0.25 m was already given as the radius).

✅ Correct Answer

The block is constantly changing direction (moving in a circle at constant speed). According to Newton's First Law, an object moving in a straight line continues at constant velocity unless acted upon by a resultant force; therefore, because its velocity vector changes direction, a resultant force must be acting.

🧠 Exam Technique

Examiners require a two-part answer: (1) State the observable kinematic change (changing direction/velocity), and (2) Explicitly link it to Newton's First or Second Law.

❌ Common Errors

Writing "changing velocity" without specifying that the direction is changing is insufficient for the first mark point, because constant speed can imply constant velocity if direction isn't mentioned.

✅ Correct Answer

1.55 m (Using standard g = 9.81 N kg⁻¹ )

💡 Key Knowledge

For the shadow of the pendulum to stay in phase with the block's shadow, their time periods must be identical. Pendulum period formula: T = 2π √(l / g) .

📐 Calculation Steps

1. Equate periods: T = 2.50 s
2. Rearrange pendulum equation for length ( l ): l = g (T / 2π)²
3. Substitute values ( g = 9.81 ): l = 9.81 × (2.50 / (2π))²
4. Evaluate: l = 1.549... m rounds to 1.55 m

❌ Common Errors

Using g = 10 N kg⁻¹ yields 1.58 m , which examiners do not award full marks to if standard A-Level constants ( 9.81 ) are expected. Watch out for proper algebraic rearrangement before substitution.

✅ Correct Answer

Amplitude: The pendulum shadow amplitude becomes less than the block shadow amplitude.
Phase: Time period changes (or frequency increases as pendulum amplitude decreases), therefore the shadows go out of phase.

💡 Key Knowledge

Air resistance introduces light damping to the pendulum, causing its amplitude of oscillation to decay over time. For a simple pendulum, isochrony holds for small angles, but decay affects energy and can alter effective timing characteristics if compared dynamically over extended cycles.

🧠 Exam Technique

Make sure you provide explicit comparisons for both properties: state clearly that the pendulum shadow gets smaller relative to the block, and explain why the phase relationship breaks down.