4.8 Calculating Acceleration from Velocity and Time
reaches the bottom. If it takes him 5 seconds to reach the bottom, what is his average acceleration as he races down
the hill?
acceleration=
∆v
∆t
=6 m/s−1 m/s
5 s
=
5 m/s
5 s
=1 m/s
1 s
=1 m/s^2In words, this means that for each second the cyclist travels downhill, his velocity (in this case, his speed) increases
by 1 meter per second on average. Note that the answer to this problem is expressed in m/s^2 , which is the SI unit for
acceleration.
FIGURE 4.10
Q:The cyclist slows down at the end of the race. His velocity changes from 6 m/s to 2 m/s during a period of 4
seconds without any change in direction. What was his average acceleration during these 4 seconds?
A:Use the equation given above for acceleration:
acceleration=
∆v
∆t
=6 m/s−2 m/s
4 s
=
4 m/s
4 s
=
1 m/s
1 s
=1 m/s^2