A Level H2 Physics Mechanics Quiz

A-Level Physics H2 Quiz - Mechanics (Answers)

Section A: Short Answer Questions [8 marks]

1. State the principle of conservation of linear momentum. [2] Answer: In a closed system (or isolated system), the total momentum before an event equals the total momentum after the event, provided no external forces act. [2 marks] Alternative: The total momentum of a system remains constant if the net external force is zero. [2 marks]

Marking: 1 mark for system specification, 1 mark for before/after equality and external force condition.

2. Calculate the maximum acceleration. [2] Working: $a_{\max} = \omega^2 X_0$ $a_{\max} = (2.5)^2 \times 0.08 = 6.25 \times 0.08 = 0.50$ m s⁻²

Answer: 0.50 m s⁻² [2 marks]

Marking: 1 mark for correct formula, 1 mark for correct calculation and unit.

3. State Faraday's law of electromagnetic induction. [2] Answer: The induced EMF in a circuit is equal to the negative rate of change of magnetic flux through the circuit. [2 marks] Alternative: The magnitude of the induced EMF equals the rate of change of magnetic flux linkage. [2 marks]

Marking: 1 mark for EMF reference, 1 mark for rate of change of magnetic flux.

4. Calculate initial kinetic energy. [2] Working: $KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 1.5 \times (6.0)^2 = 0.75 \times 36 = 27$ J

Answer: 27 J [2 marks]

Marking: 1 mark for correct formula, 1 mark for correct calculation and unit.

Section B: Structured Questions [10 marks]

5(a) Calculate velocity after collision. [3] Working: Using conservation of momentum: $m_A u_A + m_B u_B = (m_A + m_B)v$ $(2.0 \times 3.0) + (1.5 \times 0) = (2.0 + 1.5)v$ $6.0 = 3.5v$ $v = \frac{6.0}{3.5} = 1.71$ m s⁻¹

Answer: 1.7 m s⁻¹ [3 marks]

Marking: 1 mark for conservation of momentum equation, 1 mark for correct substitution, 1 mark for correct answer.

5(b) Calculate kinetic energy lost. [3] Working: Initial KE = $\frac{1}{2} \times 2.0 \times (3.0)^2 + \frac{1}{2} \times 1.5 \times 0^2 = 9.0$ J Final KE = $\frac{1}{2} \times 3.5 \times (1.71)^2 = 5.1$ J Energy lost = $9.0 - 5.1 = 3.9$ J

Answer: 3.9 J [3 marks]

Marking: 1 mark for initial KE, 1 mark for final KE, 1 mark for correct difference.

6(a) State two precautions. [2] Answers: (i) Connect the LED with correct polarity (positive terminal to anode) [1] (ii) Start with low voltage and increase gradually to avoid damaging the LED [1]

Marking: 1 mark each for appropriate circuit precautions.

6(b) Explain threshold voltage effect. [2] Answer: When the applied voltage is below 1.8 V, the LED does not conduct current / no current flows through the LED / the LED does not light up. This is because the voltage is insufficient to overcome the potential barrier in the p-n junction. [2 marks]

Marking: 1 mark for no conduction/current, 1 mark for explanation of potential barrier.

Section C: Extended Response [7 marks]

7(a) State three precautions with explanations. [6]

Sample Answers: Precaution 1: Use a small amplitude (less than 15°) / Ensure small angle oscillations Explanation: This ensures the motion approximates simple harmonic motion and the formula T = 2π√(l/g) is valid

Precaution 2: Measure the time for multiple oscillations (e.g., 20 oscillations) Explanation: This reduces the percentage error in timing and improves precision of period measurement

Precaution 3: Ensure the pendulum oscillates in a vertical plane / Avoid elliptical motion Explanation: This prevents additional forces that would affect the period and ensures accurate measurement of g

Alternative acceptable precautions:

• Use a long pendulum length / Minimize air resistance effects
• Start timing when pendulum passes through equilibrium position
• Use a rigid support / Avoid parallax when measuring length
• Keep the mass concentrated at the bottom of the string

Marking: 2 marks per precaution-explanation pair (1 mark for precaution, 1 mark for valid explanation)

7(b) State one safety precaution. [1] Answer: Ensure the pendulum cannot hit anyone when swinging / Stand clear of the pendulum path / Secure the support firmly to prevent falling [1]

Marking: 1 mark for appropriate safety measure.

Total: 25 marks