A physics problem!?

Question

A boat can move at 30km/h in still water. How long will it take to move 12 km upstream in a river flowing 6 km/h ?

(please show the steps)

Answer 1

Let's say the boat goes 30-6 or 24 km/hr against the stream

then we set up our equation

24*t = 12km

t = 12/24 or 1/2 hr

Answer 2

In a perfect theoretical sense, the speed of the boat relative to the land is the sum of the speed of the water and the speed of the boat ON the water.

For example if the boat could do 30 km/h in still water and it was trying to go upstream (against the current) on a river going 30 km/hr, the the boat would just keep up, and stay motionless compared to the land.  Going downstream on the same river the boat could go 60 km/hr relative to the shore.

In this case the boat can go 30 km/hr on still water.

The stream is 6 km hr (or -6 km hr in the direction the boat is going).  So,

30-6=24 km/h (the boat moves upstream)

to get 12 km going 24 km/hr, how long will it take

you can probably see already that it will take half an hour but to go through the math

we know rate x time = distance

so time = distance/rate

in this case time= 12 km/24 km/hr = 1/2 hrs or .5 hrs

hope that helps

The stream is going