A roller-coaster car has a mass of 493 kg when fully loaded with passengers. The path of the coaster from its initial point shown in the figure to point B involves only up-and-down motion (as seen by the riders), with no motion to the left or right. Assume the roller-coaster tracks at points and are parts of vertical circles of radius r₁ = 10.0 m and r₂ = 15.0 m, respectively.