Superman's girlfriend Lois (mass m = 62.0 kg) trips and falls from point A the top of a building (height H = 15.0 m from the ground below). At point A Lois has zero initial velocity. When Lois is at a height h = 5.00 m from the ground (point B), Superman comes to the rescue and provides an upward force F so that she reaches the ground (point C) with zero speed.
a. Use the work-kinetic energy theorem to determine Lois's speed B v at point B.
The magnitude of Lois's deceleration a during the fall from point B to point C is constant and equal to 19.6 m/s2.
b. Determine the force F exerted by Superman on Lois during her fall from point B to point C. Hint: Use Newton's second law.
c. Calculate the work Ws that Superman does on Lois during her fall from point B to point C.
d. Determine the net work Wnet done on Lois by all the forces acting on her during her fall from point B to point C. Hint: Use the work-kinetic energy theorem