# I need help with this question about vectors

LCKurtz
Homework Helper
Gold Member
OK. So what, if any, value of ##t## makes Q-P point NE? That answer is the solution to your problem. Although the problem may want to know what time of day is it, given it started at noon.

OK. So what, if any, value of ##t## makes Q-P point NE? That answer is the solution to your problem. Although the problem may want to know what time of day is it, given it started at noon.
Multiply by sin45?

LCKurtz
Homework Helper
Gold Member
Multiply by sin45?
That answer makes no sense at all. You are asked for a value of ##t## and you reply "multiply by sin45".

That answer makes no sense at all. You are asked for a value of ##t## and you reply "multiply by sin45".
sorry
well in order to be 45 degrees Q has to have the same amount of x and y values away from P
eg: if Q if 3i away from Q it should also have 3j away from P
But you have to understand this that I'm trying but I don't know how to use this information to find a t value for this problem
I do understand that Q-P was to find the distance between P and Q at a certain time t
But I don't know how to find t when Q is 45 degrees to P
I'm just having this problem because i'm not used to doing vector type questions.
If it was simple distance and time I could cope.
So please lend me a hand
Thanks to you I can this far and I really appreciate it

Mark44
Mentor
From post #42:
Now Q-P

(2+t)i + (10t-15)j
From post #43:
Yes. Finally!! Now, for what t does that point northeast? What do you require about the components for a vector to point northeast?
What relationship has to exist between the i and j coordinates for a vector to point northeast?

From post #42:

From post #43:

What relationship has to exist between the i and j coordinates for a vector to point northeast?
They have to be positive and same magnitude

LCKurtz
Homework Helper
Gold Member
They have to be positive and same magnitude
You could have answered that way back when I asked it in post #43.

So, what value of ##t##, if any, makes that happen for Q-P?

Mark44
Mentor
From post #42:
Now Q-P
.
.
.
(2+t)i + (10t-15)j
What relationship has to exist between the i and j coordinates for a vector to point northeast?
They have to be positive and same magnitude
So what do you get?

From post #42:

So what do you get?

Ok I get what your saying
As I mentioned before I'm having such a hard time due to vector with i & j form
I know if it's pointing to NE the values have to be positive and same
I just don't know how to change it or in other words the proper way to do the sum when it comes to vectors
I'm not clear about the "protocol " to change the i and j in relation with time

LCKurtz
Homework Helper
Gold Member
Put ##t=1## in your vector. Does it point NE? How about ##t = 2## or ##t=3## etc. The question is, is there any value of ##t## that gives a vector that points NE.

Put ##t=1## in your vector. Does it point NE? How about ##t = 2## or ##t=3## etc. The question is, is there any value of ##t## that gives a vector that points NE.
I get it now
I have to find out by changing t which changes the values inside the bracket
Hence giving magnitude to i & j

I completely understand
Thank you very much

(2+t)i + (10t-15)j

2+t=10t-15
t-10t=-2-15
-9t=-17
t=-17/-9
t=1.889

So that's 1hr 53min 20sec past noon
Thank you very much
And thank you for being so patient with me

LCKurtz