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# M1 Vector Question

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1. Given instead that B has speed 8 m s–1 and moves in the direction of the vector (3i + 4j),

(d) find the distance of B from P when t = 7 s.

*I understand how to do this question but there is one thing which I want to know"

In the mark scheme is changes the speed into 8/5 I undestand they did that to get V to insert into an equation but how do you change the speed of 8 into a velocity of 8/5?

Thanks.
2. (Original post by A*GLORYHUNTER)
Given instead that B has speed 8 m s–1 and moves in the direction of the vector (3i + 4j),

(d) find the distance of B from P when t = 7 s.

*I understand how to do this question but there is one thing which I want to know"

In the mark scheme is changes the speed into 8/5 I undestand they did that to get V to insert into an equation but how do you change the speed of 8 into a velocity of 8/5?

Thanks.
We use a unit vector. So we do the vector divided by its magnitude. Then we multiply this by 8. Hence (3i - 4j )/ 5 * 8 = 24/5i - 32/5j
We use a unit vector. So we do the vector divided by its magnitude. Then we multiply this by 8. Hence (3i - 4j )/ 5 * 8 = 24/5i - 32/5j
Oh I see how did you get 5 as the magnitude
4. (Original post by A*GLORYHUNTER)
Oh I see how did you get 5 as the magnitude
3^2 + 4^2 = 25. Square root 25 = 5.
3^2 + 4^2 = 25. Square root 25 = 5.
Thank you so much!

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