A single mass (m1 = 3.6 kg) hangs from a spring in a motionless elevator. The spring constant is k = 294.0 N/m. Now, three masses (m1 = 3.6 kg, m2 = 10.8 kg and m3 = 7.2) hang from three identical springs in a motionless elevator. The springs all have the same spring constant given above. Now the elevator is moving downward with a velocity of v = -2.6 m/s but accelerating upward at an acceleration of a = 3.9 m/s2. (Note: an upward acceleration when the elevator is moving down means the elevator is slowing down.) What is the magnitude of the net force on the middle mass?