Physics: Mechanics, Electromagnetism, Waves and Thermal Physics
Physics on the Yamanashi entrance science paper samples mechanics, electromagnetism, waves and thermodynamics through short calculations and graph reading. You are expected to select a law, state why it applies, and carry units correctly.
Core rules
- Newton's second law: net force equals mass times acceleration. Action–reaction pairs act on different bodies and never cancel on a single body.
- Energy and momentum are conserved separately; momentum is a vector, so assign positive and negative directions before solving collisions.
- Circuits: Kirchhoff's junction and loop rules, terminal voltage V = E − Ir, and power P = VI = I²R.
- Waves: v = fλ; for a thin lens 1/f = 1/do + 1/di under the sign convention stated in the question.
- Thermodynamics: ΔU = Q + W using the paper's sign convention, and PV = nRT for an ideal gas.
Worked example
A 2.0 kg block on a frictionless 30° incline is connected over a light pulley to a hanging 3.0 kg mass. With g = 9.8 m/s², the driving force is 3.0g − 2.0g sin30° = 29.4 − 9.8 = 19.6 N. The accelerated total mass is 5.0 kg, so a = 19.6/5.0 = 3.9 m/s². Tension from the hanging mass is T = 3.0(9.8 − 3.9) ≈ 18 N. Checking the incline block: T − 2.0g sin30° = 19.6 − 9.8 = 9.8 N, and ma = 2.0 × 3.9 ≈ 7.8 N; the small gap is rounding, so the setup is consistent.
Traps
Using g = 10 when the paper specifies 9.8, leaving centimetres instead of metres, setting normal force equal to mg on an incline, and cancelling an action–reaction pair as if it acted on one object lose marks. In lens problems a virtual image has a negative image distance under the usual convention, and heat added is not the same as internal-energy change.