4- A roller-coaster car (Fig. P6.16) has a mass of 500 kg when fully loaded with passengers. The path of the |coaster from its initial point shown in the figure to point ℗ involves only up-and-down motion (as seen by the rid- ers), with no motion to the left or right. (a) If the vehicle has a speed of 20.0 m/s at point , what is the force exerted by the track on the car at this point? (b) What is the maximum speed the vehicle can have at point ⑧ and still remain on the track? Assume the roller-coaster tracks at points and B are parts of vertical circles of radius = 10.0 m and r₂ = 15.0 m, respectively. T1 B 12