Physics: Mechanics, Waves, Electricity, and Energy
Physics in the Chiba Entrance Science exam tests mechanics, wave behavior, electricity and magnetism, energy conservation, and the interpretation of graphs and experimental data. Most items ask you to select a law, define a system, and apply it quantitatively.
Core rules
- Use Newton's second law with the net force: F_net = ma. Identify all forces on the object before substituting.
- Energy conservation applies when non-conservative work is negligible; include kinetic, gravitational potential, elastic, and thermal terms as appropriate.
- For waves, v = fλ; frequency is set by the source, while speed depends on the medium.
- Ohm's law is V = IR for an ohmic component at constant temperature; series and parallel rules follow from charge and energy conservation.
- On motion graphs, slope gives velocity or acceleration, and area gives displacement or impulse depending on the axes.
Worked example
A 2.0 kg object starts from rest and is acted on by a net force of 6.0 N for 3.0 s. Find its acceleration, final speed, and distance traveled. First, a = F_net/m = 6.0/2.0 = 3.0 m/s^2. Since acceleration is constant and initial speed is zero, v = at = 3.0 × 3.0 = 9.0 m/s. The distance is s = ½at^2 = ½ × 3.0 × 9.0 = 13.5 m. The same distance follows from average speed 4.5 m/s × 3.0 s.
Traps that cost marks
- Using an applied force as the net force while ignoring friction or weight components.
- Mixing mass and weight, especially where g is involved.
- Treating frequency as changing when a wave enters a new medium.
- Reversing series and parallel resistance rules.
- Reporting a vector quantity with no direction when direction is required.