Question

Along a straight highway a car is moving with a speed of 126 km/h if brought to a stop within a distance of 200 m. What is the retardation of the car & how long does it take for the car to stop?

Answer 1

Dear student,
we know that

v² - u² = 2as

here

v = 0 (as car comes to a halt)

u = 126 km/hr = 126 x (5/18) m/s = 35 m/s

a = retardation

and s = 200 m

so, the retardation will be

a = -u² / 2s

or

a = -(35)² / (2 x 200)

thus, we get

a = -3.0625 m/s²

now, the time taken to stop will be

(v = u + at)

t = -u/a

or

t = 35/3.0625

or

t = 11.428 s

Regards