In April 1974, John Massis of Belgium managed to move two passengerrailroad cars
ID: 1666848 • Letter: I
Question
In April 1974, John Massis of Belgium managed to move two passengerrailroad cars. He did so by clamping his teeth down on a bit thatwas attached to the cars with a rope and then leaning backwardwhile pressing his feet against the railway ties. The cars togetherweighed 900 kN (about 92 tons). Assume that he pulled with aconstant force that was 2.7 times his body weight, at an upwardangle of 34° from the horizontal. His mass was83 kg, and he moved the cars by 3 m. Neglecting any retarding forcefrom the wheel rotation, find the speed of the cars at the end ofthe pull.Explanation / Answer
mass man, m = 83 kg Weight of the man, Wm = 83*9.8 = 813.4N acceleration of gravity, g = 9.8 m/s^2 Force of cars = 900000 N theta = 34 Solve for the force exerted by the man Fman = 813.4 * 2.7 = 2196.18 Solve for the force exerted by the man in the 'x' direction Fman(x) = 2196.18cos(34) = 1820.716 F = ma, force = mass * acceleration Solve for mass of the cars mass of cars, mcar = 900000/9.8 = 91836.73 F = ma, a = F/m solve for acceleration of the cars a = Fman(x)/mcar =1820.716/91836.73 = 0.019826 m/s^2 dx = 1/2 at^2 solve for time t = 2dx/a. where dx = 3m t = 17.397 seconds vf = vi+at, vi (initial velocity) = 0 vf = at solve for final velocity vf = 0.019826 m/s^2*17.397s = 0.3449 m/s