Fig. 1.1 shows
the speed-time graph for the first 125 s of the journey of a lorry.
 |
| Speed time graph |
(a)
During
the motion shown, describe what happens to
(i)
the speed of the lorry,
For the first 25 seconds the speed
of the lorry was increasing at a constant rate. Then the rate of increase of
speed gradually slows down and at 60 seconds it becomes zero. Then for the rest
of the time from 60 s to 120 s the speed remains constant.
(ii)
the acceleration
of the lorry.
The acceleration of the lorry
was constant from 0 s to 25 s. Then from 25s the acceleration gradually slows
down and becomes zero at 60s. For the rest of the time (from 60s to 120s) the
acceleration remains zero.
(b)
Determine
the maximum speed of the lorry in m/s and in km/h.
From the
graph we can see the maximum speed achieved at 60s and the value of this
maximum speed is 25 m/s.
25 m/s =
(25/1000)km/s = 0.025 km/s = 0.025km/(1/3600)h = 0.025 x 3600 km/h = 90 km/h
speed = 25
m/s
speed = 90
km/h
