MCAT Physics 3

Question 1

A photon has a wavelength of 400 nm. What is its energy? (h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s)

Accepted Answer

4.97 × 10⁻¹⁹ J

Answer

E = hc/λ = (6.63 × 10⁻³⁴ × 3 × 10⁸) / (400 × 10⁻⁹) ≈ 4.97 × 10⁻¹⁹ J.

Question 2

An ideal gas undergoes an isothermal compression. Which of the following remains constant?

Accepted Answer

Temperature

Answer

By definition, isothermal means constant temperature; kinetic energy of molecules (∝ T) also stays constant, but 'temperature' is the direct answer.

Question 3

A wave on a string has a frequency of 50 Hz and a wavelength of 0.4 m. What is the wave speed?

Accepted Answer

20 m/s

Answer

Wave speed v = fλ = 50 × 0.4 = 20 m/s.

Question 4

A 70 kg person stands on a scale in an elevator accelerating upward at 2 m/s². What does the scale read? (g = 10 m/s²)

Accepted Answer

840 N

Answer

Normal force N = m(g + a) = 70 × (10 + 2) = 70 × 12 = 840 N.

Question 5

Light travels from glass (n = 1.5) into air (n = 1.0). If the angle of incidence is 30°, what is the angle of refraction?

Accepted Answer

48.6°

Answer

By Snell's law, n₁sinθ₁ = n₂sinθ₂: 1.5 × sin30° = 1.0 × sinθ₂, so sinθ₂ = 0.75, θ₂ ≈ 48.6°.

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