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Question
Multiple choice Question. Select the correct option.
A driver applies brakes when he sees a child on the railway track, the speed of the train reduces from 54 km/h to 18 km/h in 5 s. What is the distance travelled by train during this interval of time?
Options
52 m
50 m
25 m
80 m
Solution
50 m
Explanation:
u = 54 km/h = `54xx5/18` m/s = 15 m/s
v = 18 km/h = `18xx5/18` m/s = 5 m/s
t = 5 S; S = ?
a = `("v"-"u")/"t"=(5-15)/5` = −2 m/s2
v2 − u2 = 2aS
(5)2 − (15)2 = 2aS
S = `(25-225)/-4=(-200)/(-4)` = 50 m
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