22. The free-body diagram of the cars is shown on the right. The force exerted by John Massis is F = 2.5mg = 2.5(80 kg)(9.8 m/s 2 ) = 1960 N . Since the motion is along the horizontal x-axis, using Newton’s second law, we have Fx = F cos θ = Max , where M is the total mass of the railroad cars. Thus, the acceleration of the cars is ax =
F cos θ (1960 N) cos 30° = = 0.024 m/s 2 . M (7.0 × 105 N / 9.8 m/s 2 )
Using Eq. 2-16, the speed of the car at the end of the pull is vx = 2ax Δx = 2(0.024 m/s 2 )(1.0 m) = 0.22 m/s.
