Question

The time require to stop a car of mass 800kg moving at a speed of 20m/s over a distance 25m is

Answer 1

u = 20 m/s
v = 0
s = 25m

v^2 - u^2 = 2as
0 - 20^2 = 2×a×25
-400 = 50a
a = -400/50 = -8 m/s^2

v = u + at
0 = 20 - 8t
8t = 20
t = 20/8 = 2.5 second

It will need 2.5 second to stop the car

Answer 2

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u = 20 m/s

v = 0

s = 25m

v^2 - u^2 = 2as

0 - 20^2 = 2×a×25

-400 = 50a

a = -400/50 = -8 m/s^2

v = u + at

0 = 20 - 8t

8t = 20

t = 20/8 = 2.5 second

It will need 2.5 second to stop the car.