physics
posted by scott .
A freight train has a mass of 3.1 × 107 kg.
If the locomotive can exert a constant pull
of 4.9 × 105 N, how long would it take to
increase the speed of the train from rest to
71.9 km/h? Disregard friction.

a=F/m=4.9*10^5 / 3.1*10^7=0.0158 m/s^2.
V = 71.9km/h = 71900m/3600s = 20 m/s.
t = (VVo)/a = (200)/0.0158 = 1265.8 s.
= 21 min.
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