OAT Physics Principles 2 — Questions and Answers
Question 1: A projectile is launched horizontally from a cliff 80 m high with an initial speed of 20 m/s. How far from the base of the cliff does it land? (g = 10 m/s²)
- 40 m
- 80 m (Correct answer)
- 160 m
- 200 m
Correct answer: 80 m
Time to fall: t = √(2h/g) = √16 = 4 s; horizontal range = 20 × 4 = 80 m.
Question 2: Which of the following best describes the work done by a centripetal force on an object moving in a circular path?
- Positive work equal to the kinetic energy
- Negative work equal to the potential energy change
- Zero, because force is perpendicular to velocity (Correct answer)
- Positive work proportional to the radius
Correct answer: Zero, because force is perpendicular to velocity
Centripetal force always points toward the center, perpendicular to the velocity, so it does no work on the object.
Question 3: An ideal gas undergoes an isothermal expansion. Which statement is correct?
- Internal energy increases as volume increases
- The gas does positive work and absorbs heat from surroundings (Correct answer)
- Pressure increases as volume increases
- Temperature rises as the gas expands
Correct answer: The gas does positive work and absorbs heat from surroundings
In an isothermal process, internal energy is constant, so by the first law, heat absorbed equals work done by the gas.
Question 4: Two parallel plates separated by 0.01 m create a uniform electric field. If a proton (charge 1.6 × 10⁻¹⁹ C) accelerates through a potential difference of 100 V, what is its gain in kinetic energy?
- 1.6 × 10⁻¹⁷ J (Correct answer)
- 1.6 × 10⁻¹⁹ J
- 1.6 × 10⁻²¹ J
- 1.0 × 10⁻¹⁷ J
Correct answer: 1.6 × 10⁻¹⁷ J
ΔKE = qΔV = (1.6 × 10⁻¹⁹ C)(100 V) = 1.6 × 10⁻¹⁷ J.
Question 5: Light travels from glass (n = 1.5) into air (n = 1.0). What is the critical angle for total internal reflection?
- 19.5°
- 41.8° (Correct answer)
- 48.6°
- 56.4°
Correct answer: 41.8°
sin θ_c = n₂/n₁ = 1.0/1.5 = 0.667, so θ_c = sin⁻¹(0.667) ≈ 41.8°.
Question 6: A wave on a string has a frequency of 5 Hz and a wavelength of 0.4 m. What is the wave speed?
- 0.08 m/s
- 0.5 m/s
- 2 m/s (Correct answer)
- 12.5 m/s
Correct answer: 2 m/s
Wave speed v = fλ = 5 Hz × 0.4 m = 2 m/s.
Question 7: A 2 kg object on a frictionless surface is attached to a spring (k = 200 N/m) and displaced 0.1 m from equilibrium. What is the maximum kinetic energy during oscillation?
- 0.5 J
- 1 J (Correct answer)
- 2 J
- 4 J
Correct answer: 1 J
Maximum KE equals maximum PE = ½kx² = ½(200)(0.1)² = 1 J.
OAT Physics Principles 2
A projectile is launched horizontally from a cliff 80 m high with an initial speed of 20 m/s.
How far from the base of the cliff does it land? (g = 10 m/s²)