Two people start from the same point. One walks east at 5 mi/h and the other walks northeast at 7 mi/h. How fast is the distance between the people changing after 15 minutes? (Round your answer to three decimal places.)

Answer 1

At time t, using the law of cosines,

d^2 = (7t)^2 + (5t)^2 - 2(5t)(7t)cosπ/4
= 74t^2 - 35√2 t^2
= (74-35√2)t^2

so,
2d dd/dt = 2(74-35√2)t

Now, plug in your numbers to get d(15), and solve for dd/dt at t=15

Remember to use appropriate units

Answer 2

17

Answer 3

Two people start from the same point. One walks east at 6 mi/h and the other walks northeast at 8 mi/h. How fast is the distance between the people changing after 15 minutes? (Round your answer to three decimal places.)