A student's backpack, full of textbooks, is hung from a spring scale attached to the ceiling of an elevator. When the elevator is accelerating downward at 3.9 m/s', the scale reads 57 N. What is the mass of the backpack (in kg)? 9.66 ) What does the scale read (in N) if the elevator moves upward while slowing down at a rate 3.9 m/s2? 64.66 X IN What does the scale read (in N) if the elevator moves upward at constant velocity? 132.34 X Z (d) If the elevator had no brakes and the cable supporting it were to break loose so that the elevator could fall freely, what would the spring scale read (in N)? N