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9 multiple-choice questions and 17 flashcards on Work, Energy, and Power, about 6% of the High School Physics bank. Every one carries a written rationale.
Work, Energy, and Power is one of 11 chapters in CoStudy's High School Physics bank, and it holds 9 of the bank's 150 multiple-choice questions — roughly 6% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
7 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
What is the KINETIC ENERGY of a 2 kg object moving at 4 m/s?
Answer: E — 16 J (KE = ½mv² = ½ × 2 × 16 = 16 J)
KE = (1/2)mv² = (1/2)(2)(4²) = (1/2)(2)(16) = 16 J. KE scales with velocity SQUARED. Double the speed = quadruple the KE. Foundation of energy.
What is the unit of FREQUENCY?
Answer: D — Hertz (Hz; cycles per second; 1 Hz = 1/s)
Frequency: f = 1/T (period). Unit: Hz = 1/s. Examples: 60 Hz AC power, 440 Hz musical A, MHz/GHz for radio. f and wavelength inversely related (v = fλ).
Which is an example of TRANSFORMER's function?
Answer: D — Steps up or down AC voltage via electromagnetic induction (primary/secondary coils, different turn counts; conservation of power)
Transformers: AC voltage conversion via Faraday's law of induction. V_secondary/V_primary = N_secondary/N_primary. Power approx conserved (P = VI). Step up = increase voltage decrease current. Used in power transmission (high V, low I = low resistive losses).
Conservation of energy: if 100 J of potential energy converts to kinetic, the total mechanical energy is:
Answer: C — 100 J (constant — energy conserved in closed system; PE ↔ KE conversion preserves total)
Conservation of mechanical energy (no friction): PE + KE = constant. If 100 J PE → 100 J KE, total is still 100 J. Energy converts forms but total preserved. Foundation of physics. Includes thermal energy if friction.
What is the FIRST LAW of thermodynamics?
Answer: A — Energy is conserved: ΔU = Q + W (internal energy change = heat added + work done on system)
Thermodynamics laws: 0th (thermal equilibrium), 1st (energy conservation; ΔU = Q + W or Q - W depending on sign convention), 2nd (entropy increases in isolated system), 3rd (absolute zero unreachable). Memorize 1st-3rd.
What is the unit of energy in SI?
Answer: D — Joule (J = N·m = kg·m²/s²)
Energy in SI: joules (J). J = N·m (force × distance) = kg·m²/s². Watt = J/s (power). Other energy units: kWh, calorie, eV (1 eV ≈ 1.6×10⁻¹⁹ J). Important to know SI units.
What does the DOPPLER EFFECT describe?
Answer: A — Apparent change in frequency/wavelength of waves due to relative motion between source and observer; common: ambulance siren pitch change
Doppler effect: f_observed > f_source if approaching, < if receding. Common with sound (siren), light (redshift of distant galaxies). Used in radar, ultrasound, astronomy (cosmological redshift). Christian Doppler 1842.
4 cards from the 17 in this chapter.
Without friction, what is conserved as a ball rolls down a hill?
Mechanical energy: KE + PE = constant.
WORKED EXAMPLE — Work-energy theorem (W = ΔKE): A 4 kg cart moving at 3 m/s is pushed by 12 N over 5 m (along motion, no friction). Find the final speed.
STEP 1 — Initial KE: KE_i = ½mv_i² = ½·4·3² = ½·4·9 = 18 J. STEP 2 — Work done: W = F·d = 12·5 = 60 J. STEP 3 — Work-energy theorem: W = ΔKE → KE_f = KE_i + W = 18 + 60 = 78 J. STEP 4 — Solve for v_f: ½·4·v_f² = 78 → v_f² = 39 → v_f = √39 ≈ 6.24 m/s. ANSWER: v_f ≈ 6.24 m/s.
What is elastic potential energy in a spring?
PE = ½kx², where k is the spring constant and x is the displacement from equilibrium.
An object of mass 3 kg sits at height 5 m. What is its gravitational PE?
PE = mgh = 3 × 9.8 × 5 = 147 J.
These are a sample. The full Work, Energy, and Power chapter runs 26 items with per-chapter progress tracking, on the web and in the iOS app.