Complete question :
A driver of a car moving with speed 90km/h saw a child on the road 25m ahead of him .he jammed on the brake and bought the car to rest. Calculate the time taken to bring the car to rest and retradation of the car.
Answer:
t = 2 seconds ; retradation = - 12.5 m/s²
Step-by-step explanation:
Given that :
Final velocity v = 0
Initial Velocity u = 90 km /hr = (90 * 1000)m / 3600s = 90000m/3600s = 25m/s
Distance = 25 m
Using the relation :
v² = u² + 2aS
where, S = distance covered a = retradation
0 = 25² + 2a(25)
0 = 625 + 50a
50a = - 625
a = - 12.5 m/s²
Time taken (t) :
Using :
v = u + at
0 = 25 + (-12.5 * t)
0 = 25 - 12.5t
12.5t = 25
t = 25 / 12.5
t = 2 seconds