As shown in the figure, a roller-coaster track includes a circular loop of radius R in a vertical plane. A car of mass m is released from rest at a height h above the bottom of the circular section and then moves freely along the track with negligible energy loss due to friction. No (a) First suppose the car barely makes it around the loop; at the top of the loop, the riders are upside down and feel weightless. Find the required height h of the release point above the bottom of the loop. (Use any variable or symbol stated above along with the following as necessary: g.) h = (b) If the car is released at some point above the minimum required height, determine the amount by which the normal force on the car at the bottom of the loop exceeds the normal force on the car at the top of the loop. (Consider the moments when the car reaches the top and when it reaches the bottom again. Use any variable or symbol stated above along with the following as necessary: g.) NB - N =