An inspector provides the student with the following graph showing the acceleration a of the elevator as a function of time t . 2.0- -Timer s) Acceleration ( m / ) 10- 12- 20- -1.0- C. During what time interval ( s) is the force exerted by the platform scale on the student a maximum value ? D. Calculate the magnitude of that maximum force for a 45 kg student . E. During what time interval (s ) is the speed of the elevator constant ?