升降机由静止开始以加速度a₁匀加速上升2s，速度达到3m/s；接着匀速上升10s；最后再以加速度a₂匀减速上升3s才停下来．求：

（l）匀加速上升的加速度a₁

（2）匀减速上升的加速度a₂

（3）上升的总高度H．（画出v-t图象然后求出总高度）

Traditionally，the signal for fire aboard ship is（）.

A.more than 6 short blasts and 1 long blast on the whistle，and the same signal on the general alarm

B.continuous sounding of the ship's whistle and the general alarm for at least 10 seconds

C.1 short blast on the whistle

D.alternating short and long blasts on the ship's whistle