physics
posted by smh .
A freight train has a mass of 1.5 107 kg. If the locomotive can exert a constant pull of 6.9 105 N, how long does it take to increase the speed of the train from rest to 72 km/h?
min

i assume you mean the mass is
M = 1.5*10^7 kg
The acceleration is
a = F/M = 6.9*10^5/1.5*10^7 = 0.046 m/s^2
72 km/h = 20 m/s
Divide 20 m/s by the acceleration rate to get the time required.
T = (20 m/s)/(0.046 m/s^2) = _____ s