While an elevator of mass $2530 \mathrm{kg}$ moves upward, the force exerted by the cable is $33.6 \mathrm{kN} .$ (a) What is the acceleration of the elevator? (b) If at some point in the motion the velocity of the elevator is $1.20 \mathrm{m} / \mathrm{s}$ upward, what is the elevator's velocity 4.00 s later?