Question

The rolling resistance of steel is typically mu_r = .002. If a train weighing 160,000 kg is rolling at 12m/s and the engineer turns off the engine to let the train cruise to a stop, how much time will it take to come to a stop? How far will the train move during this time? What is the drag force on a 1.5 m wide, 1.8 m high car traveling at 20 m/s? A 22 cm diameter bowling ball has a terminal speed of 77 m/s. What is the balls mass? A 1600 kg truck pushes a 2200 kg SUV that has a dead battery. If the truck can push against the ground with a force of 4800 N, what is the magnitude of the force of the truck on the SUV.

Answer 1

The frictional force will be:

Ff = 160,000 x 9.8 x 0.002 = 3136 N

acceleration would be:

a = Ff/m = 3136/160000 = 0.0196 m/s^2

we know that, a = v/t => t = v/a

t = 12/0.0196 = 612.2 sec

The distance travelled will be:

D = Vavg x t = 12/2 x 612.2 = 3673.5 m

Hence, t = 612.2 s and D = 3673.5 m.