A box of mass = 50 kg, which was initially at rest, is lifted vertically upwards by a rope exerting an unknown tension force against the gravitational force on the box. The box moves up with an acceleration a = 6 m/s^2. Find:
a) The tension force on the box is _____ Newton.
b) If the box is lifted up for a time t = 4 seconds, the work done by the tension force on the box is _______ Joules.
c) The work done by the gravitational force on the box in a time t = 4 seconds is ______ Joules.