13. Bob takes a bathroom scale into an elevator. (A bathroom scale measures the normal force it must exert to support your weight- that's why it shifts if you shift your weight while standing on it.) He pushes the button to go up. As the elevator accelerates upward, the scale reads 1100 N (its metric & in proper SI units!). When the elevator moves upward at constant speed, the scale reads 804 N. As it slows down, approaching Bob's floor, the scale reads 524 N. a) What is Bob's mass? (Hint: think about which of the three periods in the elevator could provide that information given only the scale reading) b) What is the acceleration of the elevator as it begins to move? c) What is the acceleration of the elevator as it slows down?