in 1 minute and 20 seconds. Find her average speed and the
magnitude of her average velocity.Here’s How to Crack It
Average speed is total distance divided by elapsed time. Since the length of the
track is 500 m, the runner’s average speed was (500 m)/(80 s) = 6.3 m/s. However,
since her displacement was zero, her average velocity was zero also: v = ∆s/∆t =
(0 m)/(80 s) = 0 m/s.
- Is it possible to move with constant speed but not constant
velocity? Is it possible to move with constant velocity but not
constant speed?
Here’s How to Crack It
The answer to the first question is yes. For example, if you set your car’s cruise
control at 55 miles per hour but turn the steering wheel to follow a curved section
of road, then the direction of your velocity changes (which means your velocity is
not constant), even though your speed doesn’t change.
The answer to the second question is no. Velocity means speed and direction; if the
velocity is constant, then that means both speed and direction are constant. If speed
were to change, then the velocity vector’s magnitude would change (by definition),
which immediately implies that the vector changes.