The difference between speed and velocity
2 marks · EasyAn athlete runs around a circular track at constant speed. Explain why the athlete’s velocity is not constant.
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Because the direction of motion changes, so velocity (which depends on direction) changes even though speed stays the same.
Also accept: Velocity includes direction, which is changing as the athlete runs the curve.; Even with constant speed, changing direction means changing velocity.
Common mistakes: Saying only 'because speed is constant'; Not mentioning direction
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States velocity depends on direction (vector property).
B2 · 1 mark · Explains that running in a circle means direction is always changing.
Worked solution
Although the speed is constant, the direction keeps changing as the athlete runs around the curve. Because velocity includes direction, the velocity changes whenever direction changes.