You are Here: Home >< Maths

# M1 vectors q help pleasse watch

1. A particle P starts at the point with position vector Ro P moves with constant velocity vms after t seconds P is at point with position vector r

Find t if Ro = 4i+j r= 12i-11j and v= 2i-3j

a bit confused answer is t=4 but not sure how to get there if anyone could explain that would really help thankss !

also find t if Ro = -2i+3j R= 6i-3j and the speed of P is 4ms-1 ?!
2. Not sure if you're still stuck on this problem, but I'll point you (and and anyone else that stumbles onto this thread) in the right direction:

You know that the final position vector is equal to the initial postion vector plus the velocity multiplied by the time, given by so you can just sub the given values into the equation.

This leaves you with

It should be relatively straightforward, now, to work out t.

For the second question, you know that the modulus (absolute value) of a given velocity is its speed. Extending this logic, you can take the modulus of the entire equation to find the speed as working out the velocity and subbing it in is not an option. Remembering that , you can mod the equation leaving you with

EDIT: I may have told a fib at the end, I don't think its but rather, . Not too sure though, perhaps someone can check it and confirm.
3. (Original post by lebron_23)
Not sure if you're still stuck on this problem, but I'll point you (and and anyone else that stumbles onto this thread) in the right direction:

You know that the final position vector is equal to the initial postion vector plus the velocity multiplied by the time, given by so you can just sub the given values into the equation.

This leaves you with

It should be relatively straightforward, now, to work out t.

For the second question, you know that the modulus (absolute value) of a given velocity is its speed. Extending this logic, you can take the modulus of the entire equation to find the speed as working out the velocity and subbing it in is not an option. Remembering that , you can mod the equation leaving you with

EDIT: I may have told a fib at the end, I don't think its but rather, . Not too sure though, perhaps someone can check it and confirm.
After getting to find t simply make the i components equal so this should lead to the correct answer OP

EDIT: It should work when making j components equal too

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 30, 2013
Today on TSR

### Exam Jam 2018

Join thousands of students this half term

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams