黑龙江省被誉为（　　）

    Tom always can't sleep well at night. But he was never late for work. He went to see his doctor on Sunday afternoon. He took the subway to get there. He met his boss on the subway and they talked for a while.

    Tom got some sleeping pills from the doctor. That night Tom took the pills. He had a nice sleep. He went to work happily on foot in the morning. Getting into the office, he said to his boss “I had a nice sleep and got up happily this morning.” “That's fine,” shouted the boss, “but where were you on Monday?”

某运动员做跳伞训练，他从悬停在空中的直升飞机上由静止跳下，跳离飞机一段时间后打开降落伞做减速下落．他打开降落伞后的速度图线如图a．降落伞用8根对称的绳悬挂运动员，每根绳与中轴线的夹角均为37°，如图b．已知人的质量为50kg，降落伞质量也为50kg，不计人所受的阻力，打开伞后伞所受阻力f与速度v成正比，即f=kv （g取10m/s2，sin53°=0.8，cos53°=0.6）．求：