Motion Problems: jet ski going with, against current

[danaethorn]

Robert has a jet ski that will travel at the rate of 35 mph in still water. He can go 50 miles up a river in the same amount of time if takes him to go 75 miles down the river

1. How fast can Robert travel going down the river?

2. What is the total time required for Robert to make this trip?

 

[galactus]

Re: Motion Problems

The idea here is to find the rate of the current. Let r=35 and c=current rate. That way when he is going upstream he is going against it and his rate would be r-c. If he is going with the current(downstream), then his rate would be r+c. Using t=d/r

\(\displaystyle \frac{50}{35-r}=\frac{75}{35+r}\)

Solve for r.