An elevator is stopped at the ground floor. It starts moving upwards at constant acceleration a>0 for 5 seconds. It then keeps a constant speed for 35 seconds. Finally, it slows down with an acceleration of the same magnitude (but opposite direction) −a , until it comes to a halt at the top floor. The top floor is 450 meters above the ground floor.

(a) What is the maximal speed v of the
elevator ? (in m/s)

(b) What is the acceleration a ? (in m/s2)