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评分标准分析 — Gravitational Fields

常见 Command Words 及得分要点​

"Define gravitational field strength"​

  • B1: force per unit mass
  • 必须包含 force 和 per unit mass

"Define gravitational potential"​

  • B1: work done per unit mass
  • B1: (in bringing a small test mass) from infinity (to the point)

"State Newton's law of gravitation"​

  • M1: F=Gm1m2/r2F = Gm_1m_2/r^2
  • A1: 说明 GG 是 gravitational constant

"Show that" 轨道周期​

  • B1: gravitational force provides the centripetal force
  • M1: GMm/r2=mrω2GMm/r^2 = mr\omega^2 and ω=2π/T\omega = 2\pi/T
  • A1: 完成代数推导

典型 MS 表达​

表达得分
"(gravitational) force provides the centripetal force/acceleration"B1
"force per unit mass"B1
"work done per unit mass . . . from infinity"M1, A1
"orbit above the Equator"B1
"west to east"B1

常见 ECF 情况​

  • 引力势公式写错符号（正号）— 不扣分如果后续使用一致
  • 计算轨道半径时 rr 单位错误（km 未转 m）— 后续 ECF