M1 help vectors!

Hey guys I was just wondering about this question. i managed to answer it all fine apart from the last question where on the mark scheme they took L away from S but i took S away from L to get the position vector of S relative to L. my answer for T was the same so i guess my real question is if your way is not on the mark scheme would you get method marks for it? im bad at explaining so if it helps i put (9-3t)^2 + (12-4t)^2 =100 whereas they put (3t-9)^2 + (4t-12)^2 =100 .anyway the question is below you proberly wont need it to answer my question but oh well. p.s sorry for asking such a simple question in such a long way

A ship S is moving along a straight line with constant velocity. At time t hours the position vector of S is s km.When t= 0, s= 9i– 6j. When t= 4, s= 21i+ 10j.

(c) Show that s=(3t + 9) i + (4t– 6) j

A lighthouse Lis located at the point with position vector
(18i+ 6j)km. When t=T, the ship S is 10km from L.

(d) Find the possible values of T

Reply 1

SFin

Original post by randymarsh

Hey guys I was just wondering about this question. i managed to answer it all fine apart from the last question where on the mark scheme they took L away from S but i took S away from L to get the position vector of S relative to L. my answer for T was the same so i guess my real question is if your way is not on the mark scheme would you get method marks for it? im bad at explaining so if it helps i put (9-3t)^2 + (12-4t)^2 =100 whereas they put (3t-9)^2 + (4t-12)^2 =100 .anyway the question is below you proberly wont need it to answer my question but oh well. p.s sorry for asking such a simple question in such a long way

A ship S is moving along a straight line with constant velocity. At time t hours the position vector of S is s km.When t= 0, s= 9i– 6j. When t= 4, s= 21i+ 10j.

(c) Show that s=(3t + 9) i + (4t– 6) j

A lighthouse Lis located at the point with position vector
(18i+ 6j)km. When t=T, the ship S is 10km from L.

(d) Find the possible values of T

What you have done is the exact same thing so it would be fine.

Reply 2

Davelittle

13

Original post by randymarsh

Hey guys I was just wondering about this question. i managed to answer it all fine apart from the last question where on the mark scheme they took L away from S but i took S away from L to get the position vector of S relative to L. my answer for T was the same so i guess my real question is if your way is not on the mark scheme would you get method marks for it? im bad at explaining so if it helps i put (9-3t)^2 + (12-4t)^2 =100 whereas they put (3t-9)^2 + (4t-12)^2 =100 .anyway the question is below you proberly wont need it to answer my question but oh well. p.s sorry for asking such a simple question in such a long way

A ship S is moving along a straight line with constant velocity. At time t hours the position vector of S is s km.When t= 0, s= 9i– 6j. When t= 4, s= 21i+ 10j.

(c) Show that s=(3t + 9) i + (4t– 6) j

A lighthouse Lis located at the point with position vector
(18i+ 6j)km. When t=T, the ship S is 10km from L.

(d) Find the possible values of T

Idk if it's because it's on the computer or whatever but how do you do part c) I can't think how I would go about it :/