Question

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Two bikers start at the same place and same time. The first biker rides east at a constant velocity of 5 miles per hour and the second biker rides north at a constant velocity of 12 miles per hour. Approximately how fast (in mph) is the distance between them changing after 3 hours?

A. 5
B. 7
C. 12
D. 13
E. 17

Answer 1

9514 1404 393

Answer:

D. 13

Explanation:

The distance between the bikers is the hypotenuse of a right triangle whose legs are a linear function of time. It will be ...

d(t) = √((5t)² +(12t)²) = √((25 +144)t²) = 13t

The distance between the bikers is increasing at the constant rate of 13 miles per hour. The rate is still 13 miles per hour after 3 hours.