Physics

Problem

A boy walks

100\,\text{m}

2\,\text{m/s}

and then another

100\,\text{m}

4\,\text{m/s}

. Which statement about his average speed for the whole walk is correct? a) It is

3\,\text{m/s}

, the arithmetic mean of the two speeds. b) It is about

2.86\,\text{m/s}

, obtained by taking the total time as

70\,\text{s}

. c) It is

2.67\,\text{m/s}

, which is less than the arithmetic mean of the two speeds. d) It is

2\,\text{m/s}

, the lower speed, because he walked longer at this speed.