A2L Item 161

• Description: Determine the speed of a runner who overtakes a slower runner.
• Goal: Problem solving with kinematics
• Source: CT151.2-4
• Keywords: Mechanics, Velocity

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The question for students:

Ann is running with a constant speed of 3 m/s on a straight track. Deb is also running with constant speed but is initially 10 m behind Ann. If Deb catches up to Ann after Deb has traveled 55 m, how fast is Deb running?

1. 3.2 m/s
2. 3.55 m/s
3. 3.75 m/s
4. 4.15 m/s
5. More than 4.2 m/s
6. none of the above
7. cannot be determined

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Commentary for teachers:

Answer

(6) The correct speed is 3.67 m/s. Students indicating #2 or #3 are likely making an arithmetic error. Have students graph the position vs. time graphs for each runner.

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