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评分标准分析 — Motion in a Circle

常见 Command Words 及得分要点​

"Define the radian"​

  • 角度(angle)对应的弧长(arc length)等于半径(radius)时，该角度为 1 弧度
  • B1: 必须有 arc length = radius

"Show that" / "Calculate" 向心力​

  • C1: 写出公式 F=mrω2F = mr\omega^2 或 F=mv2/rF = mv^2/r
  • C1: 代入数值
  • A1: 正确答案，含单位

"Explain why centripetal force is needed"​

  • B1: (resultant) force is perpendicular to velocity/direction of motion
  • B1: force causes change in direction (not speed)
  • B1: force directed towards centre of circle

典型 MS 表达​

表达得分
"(resultant) force provides the centripetal force"B1
"(all) forces are equal and opposite" (平衡时)B1
"force perpendicular to velocity / direction of motion"B1
"acceleration towards centre of circle"B1

Error Carried Forward (ECF)​

  • 只要后续计算与前面错误一致，ECF 适用
  • 物理方程错误(XP)不适用 ECF