Physics Principles Flashcards

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)

Answer: 80 m

Time to fall: t = √(2h/g) = √16 = 4 s; horizontal range = 20 × 4 = 80 m.

Which of the following best describes the work done by a centripetal force on an object moving in a circular path?

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.

An ideal gas undergoes an isothermal expansion. Which statement is 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.

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?

Answer: 1.6 × 10⁻¹⁷ J

ΔKE = qΔV = (1.6 × 10⁻¹⁹ C)(100 V) = 1.6 × 10⁻¹⁷ J.

Light travels from glass (n = 1.5) into air (n = 1.0). What is the critical angle for total internal reflection?

Answer: 41.8°

sin θ_c = n₂/n₁ = 1.0/1.5 = 0.667, so θ_c = sin⁻¹(0.667) ≈ 41.8°.

A wave on a string has a frequency of 5 Hz and a wavelength of 0.4 m. What is the wave speed?

Answer: 2 m/s

Wave speed v = fλ = 5 Hz × 0.4 m = 2 m/s.

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?

Answer: 1 J

Maximum KE equals maximum PE = ½kx² = ½(200)(0.1)² = 1 J.