A car drives 60\text{km} at 30\text{m/s}, then 30\text{km} at 15\text{m/s}. What is its average speed for the trip?

22.5\text{m/s} Times: 60{,}000/30 = 2000\text{s} and 30{,}000/15 = 2000\text{s}. Total distance 90{,}000\text{m} in 4000\text{s}: \bar v = 90{,}000/4000 = 22.5\text{m/s}.

50\text{m/s} (incorrect arithmetic mean of speeds)

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Acemy

Displacement, Velocity, and Acceleration

AP Physics 1· difficulty 2/5

60~\text{km}

A
$50~\text{m/s}$
B
$22.5~\text{m/s}$
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C
$25~\text{m/s}$
D
$20~\text{m/s}$

Explanation

60{,}000/30 = 2000~\text{s}

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