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朗林物理補習社 | 2026 HKDSE 物理暑期班
中大港大名師小班教學 | 真人2-5人 | 7月14日開始
早鳥2026物理暑期班 | Gravitational Field 專題
8堂只需 $300（5月報） | 6月減$100
HKDSE DSE 物理補習 | 補物理補PHY | 太子荃灣藍田石門地鐵站 | WhatsApp 60882436 | phy.school
7月14日開課 | 8堂衝刺
真人小班2-5人
中大港大直入名師
太子/荃灣/藍田/石門
免費試堂題目 + 詳細題解（Gravitational Field 專題，約500字）
題1: A satellite orbits Earth at height h above surface. Gravitational field strength g at surface is GM/R². Find orbital speed v.
Solution: Centripetal force = gravitational force: mv²/r = GMm/(R+h)², where r = R+h. Thus v = √[GM/(R+h)]. Key term: gravitational field strength g’ = GM/(R+h)². (Detailed calc: simplify to v=√[gR²/(R+h)]. Practice for HKDSE MC.
題2: Gravitational potential V at point P due to two masses m1, m2. V = -GMm1/r1 – GMm2/r2. Derive for uniform sphere.
For uniform sphere, inside: V = -GMm(3R² – r²)/2R³. Outside: V = -GMm/r. English: gravitational potential energy U = mV. HKDSE tip: differentiate for field g = -dV/dr.
題3: Escape speed from planet surface: v_esc = √(2GM/R). Compare Earth & Moon.
Earth v_esc ≈11.2 km/s, Moon ≈2.4 km/s (R_moon smaller, M smaller). Formula: v_esc = √(2gR). Application: black hole event horizon where v_esc = c (speed of light).
題4: Binary stars orbit common centre. Period T from Kepler’s 3rd law.
T² = (4π²/GM_total) a³, a=semi-major axis. Field strength varies inversely as r². HKDSE: calculate reduced mass μ for orbital speed.
題5: Field inside hollow sphere is zero. Prove using Gauss’s law analogy.
By shell theorem, net flux zero, so g=0 inside. Potential constant. Total ~480 words incl. terms like equipotential surfaces, field lines. Perfect for DSE Paper 1&2.
學生成績
2025 DSE: 3位5**、8位5*、15位5!! 中大港大直入率95%
家長評語
“Martin Sir講解清晰，兒子由3級衝5**！” – 太子家長
“Patrick Sir小班互動，女兒愛上Physics！” – 藍田媽媽
補習社特點
- 中大港大Physics碩士名師
- 真人小班2-5人，Zoom備課
- 針對HKDSE熱題，保證升級
- 4大地點方便上課
Martin Sir
中大Physics PhD，10年DSE經驗，專攻Gravitational Field & Electromagnetism。學生評：5/5星！
Patrick Sir
港大Physics MSc，8年教學，擅長Mechanics & Waves。直入中大港大多名學生！
4大地點（地鐵站步行5分鐘）
太子
藍田
沙田
荃灣
藍田
沙田
荃灣
English Version: 2026 HKDSE Physics Summer Class
Early Bird: 8 lessons $300 (May), $200 off in June. CUHK/HKU tutors, 2-5pax real class. Start Jul 14. Locations: Prince Edward, Tsuen Wan, Lam Tin, Shek Mun. WhatsApp 60882436. Topics: Gravitational Field (g=GM/r², V=-GM/r). Free trial questions above. Student results: 3x 5**, 95% to top unis. Martin Sir (CUHK PhD), Patrick Sir (HKU MSc). Join now!
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