Physics Practice Questions
Test your understanding with carefully designed multiple-choice questions. Instant feedback and detailed explanations included.
1
A 5 kg object experiences a net force of 20 N. What is its acceleration?
Easy
Using F = ma: a = F/m = 20/5 = 4 m/s². The SI unit of force (Newton) is defined as kg·m/s², so the units work out correctly.
2
A ball is thrown horizontally at 15 m/s from a cliff 80 m high. How long does it take to hit the ground? (g = 10 m/s²)
Medium
Vertical free fall: h = ½gt² → 80 = ½(10)t² → t² = 16 → t = 4 s. The horizontal velocity does not affect vertical fall time — horizontal and vertical motions are independent.
3
Which of the following is NOT a vector quantity?
Easy
Speed is a scalar — it has magnitude only. Velocity, acceleration, and force are vectors — they have both magnitude and direction. Speed = |velocity|.
4
In the First Law of Thermodynamics (ΔU = Q − W), what does W represent?
Medium
In the convention ΔU = Q − W, W is work done BY the system on its surroundings. When a gas expands against external pressure, it does positive work W = PΔV, reducing its internal energy if no heat is added. (Some textbooks use ΔU = Q + W where W is work done ON the system.)
5
A heat engine operates between temperatures 500 K and 300 K. What is the maximum (Carnot) efficiency?
Medium
Carnot efficiency: η = 1 − T_cold/T_hot = 1 − 300/500 = 1 − 0.6 = 0.4 = 40%. No real engine can exceed this efficiency operating between these temperatures.
6
A wave has frequency 440 Hz and wavelength 0.78 m. What is its wave speed?
Easy
v = fλ = 440 × 0.78 = 343.2 m/s. This is approximately the speed of sound in air at 20°C, which makes sense for a 440 Hz sound wave (concert A).
7
Light travels from water (n=1.33) into glass (n=1.5) at an angle of 30° from normal. What happens to the light ray?
Medium
By Snell's law: n₁sinθ₁ = n₂sinθ₂. Since n₂ (1.5) > n₁ (1.33), sinθ₂ < sinθ₁, so θ₂ < 30° — the ray bends TOWARD the normal. Light bends toward the normal when entering a denser medium. Total internal reflection cannot occur here since light goes from less dense to more dense.
8
In the photoelectric effect, increasing the INTENSITY of light (same frequency) primarily increases:
Medium
Intensity determines how many photons per second hit the surface. More photons → more electrons ejected per second (higher current). But each photon still has energy E = hf, and KE_max = hf − φ depends only on frequency, not intensity. This was Einstein's key insight — frequency, not intensity, determines electron energy.
9
A spaceship travels at 0.6c. Its Lorentz factor γ is:
Hard
γ = 1/√(1−v²/c²) = 1/√(1−0.36) = 1/√0.64 = 1/0.8 = 1.25. So time runs 1.25 times slower and lengths are compressed by factor 1.25 in the direction of motion for the moving spaceship.
10
Two ice skaters (60 kg and 80 kg) push off each other from rest. The 60 kg skater moves at 4 m/s. What is the speed of the 80 kg skater?
Medium
Conservation of momentum: initial p = 0. So m₁v₁ + m₂v₂ = 0. 60(4) + 80(v₂) = 0 → v₂ = −240/80 = −3 m/s. The 80 kg skater moves at 3 m/s in the opposite direction.