Question

A runner jogs 12 km north then turns and runs 16 km east in three hours. What is his displacement? Calculate his average speed. Calculate his average velocity (including the direction).

Answer 1

From the right triangle above the displacement is:

$$x = \sqrt{12^2 + 16^2} = 20km$$

The average speed is total distance divided by total time:

$$speed = \dfrac{12km + 16km}{3h} \approx 9.3km/h$$

The average velocity is the displacement divided by total time:

$$velocity = \dfrac{20km}{3h} \approx 6.7km/h$$

The direction of the velocity is the same as the direction of the displacement $x$ (see figure).

Answer. Displacement: 20km, speed: 9.3km/h, velocity: 6.7km/h, in the direction of the displacement.