Posted by **Anonymous** on Sunday, March 2, 2008 at 11:59pm.

A boat travelling at 30km/hr relative to water is headed away from the bank of a river and downstream. The river is 1/2 km wide and flows at 6km/hr. The boat arrives at the opposite bank in 1.24 min.

I calculated the perpendicular component of the boat relative to the water as 24km/hr.

I calculated the total downstream component of the boats motion as 24 km/hr (with the parallel component of the velocity of the boat relative to the water at 18km/hr).

And I calculated the direction in which the boat moves relative to land which is 45degrees to the bank.

I need help with calculating the distance the boat moves downstream as it crosses the river.

- Physics -
**drwls**, Monday, March 3, 2008 at 5:47am
I get (0.5/1.24)*60 = 24.2 km/hr for the perpendicular component. Don't do any rounding off yet.

Parallel component of velocity, relative to water = sqrt[(30^2 - (24.2)^2] = 17.7 km/h

The parallel (downstream) velocity of the boat relative to land is 17.7 + 6 = 23.7 km/hr

The distance it drifts downstream in 1.24 minutes *(23.7 km/h)*(1h/60 min)

= 0.49 km

This agrees well with your 45 degree boat direction relative to land . The downstream drift nearly equals the river's width

- Physics -
**Anonymous**, Monday, March 3, 2008 at 6:11am
thank you for the help!

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