Motion in a straight line NCERT Solutions Class 11 Physics - Solved Exercise Question 3.6

Question 3.6

A car moving along a straight highway with speed of 126 km h-1 is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop ?

Solution:

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 X a X 200
a = - 35 X 35 / 2 X 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

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