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# Need help on position vectors question (M1) Watch

1. I'm stuck on a question on position vectors from the m1 edexcel book and as my teacher hasn't taught it, I lack understanding of vectors and find this chapter hard and would really appreciate some guidance as to where I'm going wrong.

A force 2i-jN acts on a particle of mass 2kg. If the initial velocity of the particle is i+3jms-1, find how far it moves in the first 3 seconds.

So far I've used f=ma to find the acceleration, which I got as i-0.5j and used this to find the final velocity, which I got as 4i+1.5j.
I then used s=((u+v)/2)*t but got the wrong answer! I got the answer as 14.25 but it should be 10.1m, I worked out the displacement for I and j separately before adding them together.
2. (Original post by Nida123)
I'm stuck on a question on position vectors from the m1 edexcel book and as my teacher hasn't taught it, I lack understanding of vectors and find this chapter hard and would really appreciate some guidance as to where I'm going wrong.

A force 2i-jN acts on a particle of mass 2kg. If the initial velocity of the particle is i+3jms-1, find how far it moves in the first 3 seconds.

So far I've used f=ma to find the acceleration, which I got as i-0.5j and used this to find the final velocity, which I got as 4i+1.5j.
I then used s=((u+v)/2)*t but got the wrong answer! I got the answer as 14.25 but it should be 10.1m, I worked out the displacement for I and j separately before adding them together.
First off, welcome to TSR.
Adding the displacements is where you've gone wrong.
Use pythagoras to sum the displacements - they're at right angles to each other.
3. (Original post by Nida123)
I'm stuck on a question on position vectors from the m1 edexcel book and as my teacher hasn't taught it, I lack understanding of vectors and find this chapter hard and would really appreciate some guidance as to where I'm going wrong.

A force 2i-jN acts on a particle of mass 2kg. If the initial velocity of the particle is i+3jms-1, find how far it moves in the first 3 seconds.

So far I've used f=ma to find the acceleration, which I got as i-0.5j and used this to find the final velocity, which I got as 4i+1.5j.
I then used s=((u+v)/2)*t but got the wrong answer! I got the answer as 14.25 but it should be 10.1m, I worked out the displacement for I and j separately before adding them together.
I think you should to calculate the initial velocity, the force,
acceleration and movement both in direction of vektor i, and vektor j,
then calculate the vector sum of the values you've got.
x=Vx*t+Fx/(2m)*t^2
y=Vy*t+Fy/(2m)*t^2 (Fy is negative)
r=sqrt(x^2+y^2)
4. Thanks you
5. (Original post by Nida123)
Thanks you
No prob

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