老師專欄

A merry-go-round of radius R. shown in the figure, is rotating at constant speed. The friction in its bearing is so small that it can be ignored. A sandbag of mass m is dropped onto the merry-go-round, at a position designated by r. The sandbag does not slip or roll upon contact with the merry-go-round.

上一篇我們講到2019年8月起，托福會有MyBest Scores的計分方式，今天要來談談試題本身的調整。

托福官方在北京開了一個新政發表會，說明2019年8月開始，托福iBT的考試制度有些微的變化。
第一個變化是成績單上會多一個MyBest Scores，是過去2年內該考生各科最高成績的加總：

Six roller-coaster carts pass over the same semicircular "bump." The mass M of each cart (including passenger) and the normal force n of the track on the cart at the top of each bump are given in the figures.

A roller-coaster track has six semicircular "dips" with different radii of curvature. The same roller-coaster cart rides through each dip at a different speed.

A small car of mass m and a large car of mass 4m drive along a highway at constant speed. They approach a curve of radius R. Both cars maintain the same acceleration a as they travel around the curve. How does the speed of the small car vS compare to the speed of the large car vL as they round the curve?

Six artificial satellites circle a space station at constant speed. The mass m of each satellite, distance L from the space station, and the speed v of each satellite are listed below. The satellites fire rockets that provide the force needed to maintain a circular orbit around the space station. The gravitational force is negligible.

物理(Physics)是許多人心中的痛，可能花費需多時間與心力再準備，但結果卻不盡理想；主因在於物理需要理解，並非靠死記硬背，若不能融會貫通，則學習效果必定打折扣！
其實，物理想要拿高分是有訣竅的......

老師，物理好難，我都不會，怎麼辦
老師，物理公式那麼多，我又看不懂，怎麼辦
老師，我要放棄物理了......
這是剛認識的學生時常向我抱怨的，
但我總是一貫的回覆：跟著觀念走就不難！

Webb，質量是甚麼? 重量是甚麼?
Webb，質量跟重量不一樣嗎?
Webb，感覺這都在說一個東西重不重阿?

計算機科學(computer science)為時下熱門的學科，在科技爆炸性發展的時代，學會編寫程式已經是一種趨勢。

Question:
A plane flies horizontally at an altitude of 5 km and passes directly over a tracking telescope on the ground. When the angle of elevation is π/3, this angle is decreasing at a rate of π/6 rad/min. How fast is the plane traveling at that time?