Car A travels west from an intersection at a constant speed of

MATHEMATICS · Single correct · A Level · Mathematics · Differentiation · Differentiation

Problem

60\text{ mi/h}

, passing the intersection at 1:00 P.M. Car B travels north from the same intersection at a constant speed of

45\text{ mi/h}

, passing the intersection at 1:30 P.M. How fast is the distance between the two cars changing at 2:00 P.M.? (a)

84\text{ mi/h}

(b)

61.5\text{ mi/h}

(c)

72\text{ mi/h}

(d)

75\text{ mi/h}