OAT Physics Principles 4 — Questions and Answers
Question 1: A block of mass 5 kg slides down a frictionless incline angled at 30°. What is its acceleration? (g = 10 m/s²)
- 5 m/s² (Correct answer)
- 8.66 m/s²
- 10 m/s²
- 2.5 m/s²
Correct answer: 5 m/s²
Acceleration along the incline = g sin 30° = 10 × 0.5 = 5 m/s².
Question 2: Two resistors of 6 Ω and 3 Ω are connected in parallel. What is their combined resistance?
- 9 Ω
- 4.5 Ω
- 2 Ω (Correct answer)
- 18 Ω
Correct answer: 2 Ω
1/R = 1/6 + 1/3 = 1/6 + 2/6 = 3/6 → R = 2 Ω.
Question 3: Which of the following quantities is conserved in all types of collisions?
- Kinetic energy only
- Momentum only (Correct answer)
- Both kinetic energy and momentum
- Neither kinetic energy nor momentum
Correct answer: Momentum only
Momentum is always conserved in collisions; kinetic energy is conserved only in perfectly elastic collisions.
Question 4: A glass lens immersed in water has a lower refracting power than in air. This is because:
- The refractive index of glass decreases in water
- The refractive index difference between glass and water is smaller than between glass and air (Correct answer)
- Light travels faster in glass when surrounded by water
- Water absorbs some of the refracted light
Correct answer: The refractive index difference between glass and water is smaller than between glass and air
Lens power depends on the relative refractive index (n_glass/n_medium); since n_water ≈ 1.33, the contrast with glass is less than in air (n = 1.0).
Question 5: What happens to the period of a simple pendulum if its length is quadrupled?
- It doubles (Correct answer)
- It halves
- It quadruples
- It remains the same
Correct answer: It doubles
T = 2π√(L/g); quadrupling L increases √L by a factor of 2, so the period doubles.
Question 6: A photon has energy 3.0 × 10⁻¹⁹ J. Given h = 6.63 × 10⁻³⁴ J·s and c = 3 × 10⁸ m/s, what is its wavelength?
- 220 nm
- 452 nm
- 663 nm (Correct answer)
- 900 nm
Correct answer: 663 nm
λ = hc/E = (6.63×10⁻³⁴ × 3×10⁸) / (3×10⁻¹⁹) ≈ 663 nm (red light).
Question 7: An object floats in water with 40% of its volume submerged. What is the object's density? (ρ_water = 1000 kg/m³)
- 400 kg/m³ (Correct answer)
- 600 kg/m³
- 2500 kg/m³
- 1400 kg/m³
Correct answer: 400 kg/m³
By Archimedes' principle, ρ_object/ρ_water = fraction submerged → ρ_object = 0.40 × 1000 = 400 kg/m³.
OAT Physics Principles 4
A block of mass 5 kg slides down a frictionless incline angled at 30°.
What is its acceleration? (g = 10 m/s²)