3.2.1.P8

A. I need to drive from A to C via B at total distance of Δ*L*. The distance from A to B is Δ*L*_{1}, from B to C is Δ*L*_{2}. I have time Δ*t* to get from A to C, so I figure I can make it if I average <*v*> = Δ*L*/Δt for the entire trip. Going from A to B, the traffic is heavy and I can only average a speed *v*_{1}. How fast do I have to go from B to C in order to average <*v*> for the whole trip? Write an equation expressing *v*_{2} (the speed I need to average going from B to C) in terms of the other symbols given: *v*_{1}*, *Δ*L*_{1},Δ*L*_{2}, and Δ*t*.

B. I need to drive from A to C via B. The distance from A to B is 25 miles, from B to C is 75 miles. I have 2 hours to get from A to C, so I figure I can make it if I average 50 mi/h for the entire trip. Going from A to B the traffic is heavy and I can only average 25 mi/h. How fast do I have to go from B to C in order to average 50 mi/h for the whole trip?

- 58 mi/h
- 60 mi/h
- 75 mi/h
- 100 mi/h
- Something else
- You can’t get it from the information given.

Joe Redish 9/11/16

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