An elevator descends vertically into a mine shaft to a final depth of 1.2km below the Earth’s surface.
(i) A passenger of mass 70kg stands on a weighing machine in the elevator. During the first 4.0s the elevator starts from rest and attains a constant downward speed with uniform acceleration 2.0m s−2. Calculate the reading of the weighing machine during this phase at the surface.
(ii) After the elevator reaches constant speed, it continues to descend to the final depth. Assuming uniform speed, find the reading of the weighing machine when it is at the depth of 1.2km.
(iii) Compare the two readings obtained in (i) and (ii) with the true weight of the passenger at the surface, expressing each as a percentage of the surface weight, and comment briefly on the causes of the differences.