Teaching Physics with the Physics Suite

Edward F. Redish

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Running in circles

A jogger runs around a circular track of 30 m radius shown in the figure at the right. She runs at a constant speed in a clockwise direction and completes one lap in 40 seconds.

  1. Compare the directions and magnitudes of
    • her instantaneous velocity at A,
    • her instantaneous velocity at C, and
    • her average velocity going from A to C.

  1. If the runner completes exactly one lap what is her average speed? her average velocity? Explain your answer.

  2. Is the magnitude of her average velocity from A to B bigger, smaller or equal to the magnitude of her average velocity from A to C? Explain your reasoning.
  3. For this example, which do you think is more relevant: average speed or average velocity? For whichever one you chose can you think of an example in which the other one is more relevant or interesting?

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Page last modified August 31, 2004: K06