Homework Help: physics

Posted by steeven on Saturday, May 19, 2012 at 4:17am.

(a) if a train travelling at 72km/hr is to be brought to rest in a distance of 200m then wat should be its retardation
(b) if a body starts from rest and and travels 120 m in 8th sec then wats its acceleration.

physics - drwls, Saturday, May 19, 2012 at 6:32am
(a) How do you define retardation?
Is it deceleration?
72 km/h = 20 m/s
Average velocity during deceleration = 10 m/s.
10*t = 200 m
Deceleration time t = 20 s
Deceleration rate = 20 m/s/20s
= 1 m/s^2

(b) If you are supposed to assume the acceleration rate is constant,
X(8) - X(7) = (a/2)*(64-49)
= 120
15*(a/2) = 120
a = 16 m/s^2

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