A woman on a ten-speed bike travels at 9 m/s relative to the ground as she passes a little boy on a tricycle going in the opposite direction. If the boy is travelling at 1 m/s relative to the ground, how fast does the boy appear to be moving relative to the woman?

the boy will appear to be moving at 10 m/s relative to the cyclist.

Explanation:

We need to use the concept of relative velocity (as vector quantities) due to motion in opposite directions.

If the cyclist moves at 9 m/s in one direction (let's assume positive direction in a linear axis) and the boy at 1 m/s in opposite direction, then we assign  a positive sign to the 9 m/s and a negative sign to the velocity of the boy.

The velocity difference will then be:

| 9 m/s - (-1 m/s) | = 10 m/s

Then, the boy will appear to be moving at 10 m/s relative to the cyclist.