Answer:
2.4seconds
Explanation:
A body decelerating is known to have a negative acceleration.
Acceleration is the change in velocity of a body with respect to time. Mathematically,
Acceleration = change in velocity/time
Change in velocity = final velocity - initial velocity
Acceleration = final velocity (v) - initial velocity (u) /time taken (t)
This same formula will be used as the deceleration formula i.e
Deceleration = v-u/t
Given deceleration = -4.7m/s²(negative acceleration)
v = 81km/hr = (81000/3600)m/s = 22.5m/s
u = 140km/hr = (140,000/3600)m/s = 38.8m/s
Substituting the values into the deceleration formula we have;
-4.7 = 22.5-38.8/t
-4.7 = -11.3/t
-4.7t = -11.3
t = -11.3/-4.7
t = 2.4seconds
The minimum time in which you can get your car under the 81 km/h speed limit is 2.4seconds
