Mechanics 1

iRiis

Secret Tip: Make a triangle!

I got a triangle which the northeast part is the 4kmh and the bottom part of the triangle is 3 since the current flows in an easterly direction and closed it so its a right angle but im sure thats wrong i dont know what to do.
Sorry if it sounds confusing i have no otherway of explaining what values i put for my triangle

Reply 3

no your triangle is right

Reply 4

No, the top of the triangle should be three. Tip-to-tail

Reply 5

I thought JBK was referring to the original triangle- the one you get from analysing the direction of the boat and the current in the river (as opposed to the resultant velocity)

Reply 6

Forgive the crudeness :p:

vector.JPG21.9KB

Reply 7

CkJhWs

no your triangle is right

ok thanks let me try and work it out from there and i was referring to the original triangle lol

Reply 8

lol kinda hijacked the thread there eh

Reply 9

D-Day

Forgive the crudeness :p:

now that i dont have a right angle triangle i am stumped lol could you please explain?

Reply 10

CkJhWs

lol kinda hijacked the thread there eh

could you please explain to me what do i do after i have that triangle I have no idea how to find out the resultant force. thanks.

Reply 11

Because the magnitude 4 vector is North-East that forms a 135 degree angle (180-45) with the magnitude 3 vector. Law of Cosines to find the length of the other side.

Reply 12

Hi again. I haven't done M1 in over 2 years so D-Day or someone may pull me up on something however:

I'm gathering the angle that velocity 4km/h is at is 45 deg, given in is directly north east. thus the components of this velocity are 4sin45 and 4cos45=> (4/sqr2)(i+j)km/h.

It is simple to see that other velocity is just 3i.

then put these into the resultant force diagram. add the i's and j's, thus the resultant is pythagoras of this triangle. The direction is the angle between the resultant and i.

I hope this is a) right and b) explained well.

Reply 13

D-Day

Because the magnitude 4 vector is North-East that forms a 135 degree angle (180-45) with the magnitude 3 vector. Law of Cosines to find the length of the other side.

ok and ive used the cosine rule to find out the length (if that what you mean) i got 6.56 as the final answer then how would i find out the components from there?

Reply 14

D-Day

Because the magnitude 4 vector is North-East that forms a 135 degree angle (180-45) with the magnitude 3 vector. Law of Cosines to find the length of the other side.

or what he/she said...(though the question does specify the use of component form to solve it)

Reply 15

CkJhWs

or what he/she said...(though the question does specify the use of component form to solve it)

i think you've got it because i checked my teachers answer and that was the same thanks

Reply 16