gwd2 q6

gmatziyu

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Q6:











The figure above shows thedimensions of a semicircular cross section of a one-way tunnel.  The single traffic lane is 12 feet wide andis equidistant from the sides of the tunnel. If vehicles must clear the top of the tunnel by at least ½ foot whenthey are inside the traffic lane, what should be the limit on the height ofvehicles that are allowed to use the tunnel?

A.   5½ ft
B.    7½ ft
C.    8 ½ ft
D.   9½ ft
E.    10 ft
Answer:B
请问这个题目时怎样计算的？
谢谢

yxas

圆半径R=10,1/2的lane=6，得到lane在圆里形成的长方形的宽为8，由于留出1/2的高，则为7.5ft