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Question
A truck running at 90 kmh−1, is brought to rest over a distance of 25 m. Calculate the retardation and time for which brakes are applied.
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Solution
Initial velocity = u = 90 kmh−1 = `90xx5/18` ms−1
u = 25 ms−1
Final velocity = v = 0
Distance = S = 25 m
v2 − u2 = 2aS
(0)2 − (25)2 = 2a (25)
50a = −625
(retardation) a = `(-625)/50` = −12.5 ms−2
Now, v = u + at
0 = 25 + (−12.5)t
12.5t = 25
(Time) t = `25/12.5` = 2s
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