Question

A car moving along a straight highway with speed 126km/ h is brought to a stop within a distance of 200m. What is the retardation of the car (assumed uniform) and how long does it take for the car to stop?

Answer 1

retardation is -400 m/s square and time is 2 sec

Answer 2

Answer:

Initial velocity of the car, u = 126 km/h = 35 m/s

Final velocity of the car, v = 0

Distance covered by the car before coming to rest, s = 200 m

Retardation produced in the car = a

From third equation of motion, a can be calculated as:

v2 - u2 = 2as

(0)2 - (35)2 = 2 × a × 200

a = - 35 × 35 / 2 × 200 = - 3.06 ms-2

From first equation of motion, time (t) taken by the car to stop can be obtained as:

v = u + at

t = (v - u) / a = (- 35) / (-3.06) = 11.44 s