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# M1 vectors watch

1. How do i show that 2 things will collide?

i've already set the things equal to each other and i have an expression which contains t in it but i'm not sure what to do from there
2. (Original post by thefatone)
How do i show that 2 things will collide?

i've already set the things equal to each other and i have an expression which contains t in it but i'm not sure what to do from there
Be more specific. What "things" did you set equal to each other? What expression? How many dimensions are you working in? What's your question? What things are colliding? What are you talking about?
3. (Original post by Zacken)
Be more specific. What "things" did you set equal to each other? What expression? How many dimensions are you working in? What's your question? What things are colliding? What are you talking about?
mechanics eyyyyy.....

Spoiler:
Show
This is the question
At noon a ferry F is 400m due north of an observation point O moving with constant velocity (7+7) and a speedboat S is 500m due east of O, moving with constant velocity(-3+15)

show that F and S will collide, and find the position vector of the point of collision.

so far i set F=S and got this
(500-3t)+15t=7t+(400+7t)

which simplified to
(10t-500)+(499-8t)=0

that's as far as i've gotten
4. (Original post by thefatone)
mechanics eyyyyy.....

Spoiler:
Show
This is the question
At noon a ferry F is 400m due north of an observation point O moving with constant velocity (7+7) and a speedboat S is 500m due east of O, moving with constant velocity(-3+15)

show that F and S will collide, and find the position vector of the point of collision.

so far i set F=S and got this
(500-3t)+15t=7t+(400+7t)

which simplified to
(10t-500)+(499-8t)=0

that's as far as i've gotten
How did you get 499-8t?
5. (Original post by Zacken)
How did you get 499-8t?
that's a mistake it's supposed to be 400 xD mistype
6. (Original post by thefatone)
that's a mistake it's supposed to be 400 xD mistype
So now you have and . If they both give you the same value of , then they do indeed collide and at the time .
7. (Original post by thefatone)
How do i show that 2 things will collide?

i've already set the things equal to each other and i have an expression which contains t in it but i'm not sure what to do from there
the value for t should be the same on both position vectors.

Equate the expression for the first i to the second i
Equate the expression for the first j to the second j

They collide if your value for t is the same, because the position vectors are equal to each other at the same time.
8. (Original post by Zacken)
So now you have and . If they both give you the same value of , then they do indeed collide and at the time .
(Original post by jamestg)
the value for t should be the same on both position vectors.

Equate the expression for the first i to the second i
Equate the expression for the first j to the second j

They collide if your value for t is the same, because the position vectors are equal to each other at the same time.
i see, thank you both

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