题目

如图所示是某同学研究 “小车从斜面顶端滚下过程中速度的变化 ”的实验装置，图中秒表每格为 1s，根据记录，完成下列题目： （ 1）小车通过上半段的平均速度是 ____ m / s，下半段的平均速度是 ____ m / s，全程的平均速度是 _____ m / s。 （ 2）通过上述几段路程小车的运动速度的比较，你认为在全过程的速度变化是 ____。 （ 3）在实验中，为了减小误差，斜面的倾斜度应该适当 ____些，（填 “大 ”或 “小 ”）这样可使小车运动 的时间更 _ Do’s and Don’ts in Whale(鲸) Watching     The Department of Fisheries and Oceans has developed guidelines for whale watching in Johnstone Strait, where killer whales are found on a daily basis each summer. It is strongly recommended that vessel(船只) operators follow these guidelines for all kinds of whales.     · Approach whales from the side, not from the front or the back. · Approach no closer than 100 metres, then stop the boat but keep the engine on. · Keep noise levels down — no horns, whistles or racing of engines. · Start your boat only after the whales are more than 100 metres from your vessel. · Leave the area slowly, gradually moving faster when you are more than 300 metres from the whales. · Approach and leave slowly, avoiding sudden changes in speed or direction. · Avoid disturbing groups of resting whales. · Keep at low speeds and remain in the same direction if traveling side by side with whales. · When whales are traveling close to shore, avoid crowding them near the shore or coming between the whales and the shore. · Limit the time spent with any group of whales to less than 30 minutes at a time when within 100 to 200 metres of whales. · If there is more than one vessel at the same observation spot, be sure to avoid any boat position that would result in surrounding the whales. · Work together by communicating with other vessels, and make sure that all operators are aware of the whale watching guidelines. 1.For whom is this text written?    A. Tour guides.                  B. Whale watchers.      C. Vessel operators.             D. Government officials. 2.When leaving the observation areas, the vessel should ______.    A. move close to the beach       B. increase speed gradually    C. keep its engine running slowly    D. remain at the back of the whales 3.When going side by side with whales, the vessel should ______.    A. keep moving in the same direction    B. surround the whales with other boats    C. travel closer and closer to the shore    D. take a good viewing position 4.What is the shortest safe distance from the whales?    A. 400 metres.       B. 300 metres.      C. 200 metres.      D. 100 metres.