英语分站

    2012年12月02日

　　考试类型: Mathematics > Standard Multiple Choice

　　Read the following SAT test question and then click on a button to select your answer. 

　　The stopping distance of a car is the number of feet that the car travels after the driver starts applying the brakes. The stopping distance of a certain car is directly proportional to the square of the speed of the car, in miles per hour, at the time the brakes are first applied. If the car’s stopping distance for an initial speed of  miles per hour is  feet, what is its stopping distance for an initial speed of  miles per hour?

　　A.  feet

　　B.  feet

　　C.  feet

　　D.  feet

　　E.  feet

正确答案:D

解析:

The stopping distance is directly proportional to the square of the initial speed of the car. If  represents the initial speed of the car, in miles per hour, and  represents the stopping distance, you have that the stopping distance is a function of  and that , where  is a constant. Since the car’s stopping distance is  feet for an initial speed of  miles per hour, you know that . Therefore, , and the car's stopping distance for an initial speed of  miles per hour is  feet.