Question

A motor car slows down from 72km/hr to 36 km/he over a distance of 25 m.if the brakes are applied with the same force, calculate distance traveled by the car and total time in which the car comes to rest.​

Answer 1

Given :-

A motor car slows down from 72km/hr to 36 km/he over a distance of 25 m

To Find :-

Acceleration

Time

Solution :-

We know that

1 km/h = 5/18 m/s

72 km/h = 72 × 5/18 = 4 × 5 = 20 m/s

36 km/h = 36 × 5/18 = 2 × 5 = 10 m/s

Now

v² - u² = 2as

(10)² - (20)² = 2a(25)

100 - 400 = 50a

-300 = 50a

-300/50 = a

-6/1 = a

-6 = a

Acceleration is -6 m/s

v = u + at

0 = 20 + (-6)t

0 - 20 = -6t

-20 = -6t

-20/-6 = t

20/6 = t

10/3 = t

3.33 = t