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9. (20 points) A mass m= 87 kg slides on a frictionless track that has a drop, followed by a loop-the-loop with radius R = 15.3 m and finally a flat straight section at the same height as the center of the loop (15.3 m off the ground). Since the mass would not make it around the loop if released from the height of the top of the loop it must be released above the top of the loop-the-loop height. (Assume the mass never leaves the smooth track at any point on its path.) A) What is the minimum speed the block must have at the top of the loop to make it around the loop-the-loop without leaving the track? B) If the mass has just enough speed to make it around the loop without leaving the track, what will its speed be at the bottom of the loop? C) The work done by the normal force on the mass (during the initial fall) is: positive, negative or zero? cor