Physics 12 Mid-Year Review
5. A 32.0 kg box is placed on a scale in an elevator. The total mass of the elevator plus contents is 725 kg. Suddenly, the supporting cable breaks and the elevator accelerates downwards, restricted only by emergency brakes, which drag along the walls of the shaft. While the elevator is falling the scale reads 210 N.
a) Draw a free-body diagram in the space below showing the forces acting on the box while the elevator is accelerating downwards. (2 marks)
b) What is the acceleration of the elevator? (4 marks)
c) What is the magnitude of the frictional force of the brakes against the walls of the shaft? (4 marks)