First slide

Rectilinear Motion

Question

A car moving with a speed of 40km/h can be stopped by applying the brakes after at least 2m. If the same car is moving with a speed of 80km/h, what is the minimum stopping distance?

Moderate

A

8 m
B

2 m
C

4 m
D

6 m

Solution

$e q u a t i o n o f m o t i o n, V^{2} = U^{2} - 2 a s - - - (1)$
$A p p l y i n g b r a k e s i s D e c e l e r a t i o n; i n i t i a l v e l o c i t y = 40 k m / h; d i s \tan c e S = 2 m; s u b s t i t u t e i n a b o v e e q u a t i o n, 0^{2} = {(40)}^{2} - 2 a x 2 - - - (2) t h e n i n i t i a l v e l o c i t y = 80 k m / h; d i s \tan c e = ?; s u b s t i t u t e i n e q u a t i o n (1),$
$0^{2} = {(80)}^{2} - 2 a x d - - - (3) d i v i d e e q u a t i o n (3) b y e q u a t i o n (2) d = 8 m = m i n i m u m s t o p p i n g d i s \tan c e$

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