Prof. kopp is working on an experiment located in an abandoned mine near duluth, mn. the experiment is located approximately 713 m below the surface. he went to visit the site this last summer and took a harrowing ride in a bumpy, claustrophobic elevator down to the cavern. he timed the ride to last about 90 s. compute the average speed of the elevator (in mph) as it plummeted to the bottom of the shaft.