A cyclist rides along a straight seafront: 750 m north in 150 s, then 300 m back south in 75 s…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A cyclist rides along a straight seafront: $750\ \text{m}$ north in $150\ \text{s}$ , then $300\ \text{m}$ back south in $75\ \text{s}$ .

What is her average speed for the whole ride?
What is her average velocity?

Need a reminder? The key ideaShow

Over a time $\Delta t$ :

\displaystyle \text{average speed} = \frac{\text{path length}}{\Delta t}

\displaystyle v_{\text{av}} = \frac{\Delta x}{\Delta t}

Average speed is never negative; average velocity has the sign of the displacement.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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