Vectors 7.2 Take me to the River

Answering how all those water questions work. Resultant velocity, how far down the river will you end up if you travel perpendicular to the current, what angle do you need to point your vessel in to reach directly across the river, how long will it take you. Remember that your velocity triangle and your distance triangle are SIMILAR triangles ... keep the values separate. Don't combine velocities with distances. You only need both if you are asked to find HOW LONG ...

[@marcusthompson8981]

Thank you so much Ms Havrot !

[@mshavrotscanadianuniversit6234]

I'm happy that you asked me to explain this more clearly for you ... which of course also helps others. Just like in my old classroom. There were always a few that asked questions and the others benefited from their dedication to their homework.

[@BabaSphere]

Hi Ms. Havrot, thank you so much for all your help. Miss my teacher gave us this question: "A river is 800m wide and flows eastward at 10m/s. Peter is driving a motorboat heading always perpendicular to the current. The speed of the motorboat in still water is 20m/s." He says that the time it takes to cross the river is 40 s because he is doing 800/20. I said no it should be 800/resultant speed or 22.4m/s. I don't know which one is right.

[@mshavrotscanadianuniversit6234]

The “no” answer is correct because if he always stays perpendicular to the shore he will not be going straight across the river but will be pushed downstream by the current and therefore will have to travel more than the 800 m width.

[@BabaSphere]

@@mshavrotscanadianuniversit6234 Thank you so much!

[@Johnny2tc]

Thanks for the great videos... I have 1 question. We know that you vectors have no fixed positions and therefore you can translate them. But vectors of course must be confined to some space. For example I'm ghis river example, we cannot translate the rivers vectors velocity to be on land. How do you explain the restriction of the vector??

[@Johnny2tc]

Restriction of translating the vector***

[@mshavrotscanadianuniversit6234]

The vector in a river is restricted by the banks of the river. There are many vectors in the water from bank to bank. Similarly in the air. The wind would be restricted to the airspace. Air does not penetrate the ground (generally speaking). The concept of a vector being translatable is subject to the context of the problem. 😊 So, yes, you are correct but I have never required a restriction on a vector in a word problem.

[@Johnny2tc]

@@mshavrotscanadianuniversit6234 Thank you for your great help

[@laram3988]

how come we dont change the 400m to km?

[@mshavrot_math]

I did change the metres to 0.438km