Mechanical Energy and Work
Define gravitational potential energy and state the standard formula used to calculate it.
Gravitational potential energy (Ep) is energy stored in an object due to its height in a gravitational field. Formula: Ep = mgh.
State the unit and symbol used for measuring electric current.
Amperes (or Amps), symbol: A (Current variable symbol: I).
Name the three processes by which heat energy is transferred.
Conduction, Convection, and Radiation.
Calculate the kinetic energy of a 2 kg object moving at a speed of 4 m/s.
16 J (Ek = ½mv² = 0.5 × 2 × 4²).
Explain how a voltmeter must be connected in a circuit to measure the voltage across a lamp.
It must be connected in parallel (across the lamp).
Define specific heat capacity.
The amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C.
A force of 30 N is used to push a box 5 metres along a floor. Calculate the work done.
150 J (W = Fd = 30 N × 5 m).
Calculate the resistance of a resistor if a 12 V battery causes a current of 3 A to flow through it.
4 Ω (R = V / I = 12 / 3).
Calculate the heat energy required to heat 1 kg of water (c = 4200 J/kg°C) by 10°C.
42,000 J or 42 kJ (ΔE = mcΔT = 1 × 4200 × 10).
A 0.5 kg ball is dropped from a height of 5 metres. Assuming no friction, calculate its velocity just before it hits the ground.
10 m/s. (Initial Ep = mgh = 0.5 × 10 × 5 = 25 J. Since Ek = 25 J, ½mv² = 25 → 0.25v² = 25 → v² = 100 → v = 10 m/s).
A light bulb is connected to a 12 V power supply and draws a current of 0.5 A. Calculate the total electrical energy transformed if it stays on for 2 minutes.
720 J. (First calculate Power: P = VI = 12 × 0.5 = 6 W. Then calculate Energy: E = Pt = 6 W × 120 s = 720 J).
Using kinetic particle theory, explain how thermal expansion occurs when a metal rod is heated.
Heating causes the metal particles to gain kinetic energy and vibrate faster/more vigorously. These larger vibrations cause particles to push slightly further apart, causing the solid to expand.
Explain why no mechanical work is done on a crate when a person carries it across a flat room at a constant height and constant speed.
Work is defined as W = Fd in the direction of motion. Because there is no change in height (no change in Ep) and no change in speed (no change in Ek), there is no net energy transferred to the crate.
Explain why two identical lamps connected in parallel will both glow brighter than the same two lamps connected in series to the same battery.
In parallel, each lamp receives the full supply voltage, giving higher power output per bulb. In series, the total voltage is split between the bulbs, so each gets less voltage and draws less current.
Explain why thermal energy must be added to melt ice at 0°C even though the temperature does not change during melting.
The added thermal energy is used as latent heat (fusion) to break/overcome intermolecular bonds holding particles in a rigid solid structure, rather than increasing average kinetic energy (temperature).