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# Mechanics - Vectors HELP! watch

1. 8.
At time t = 0, a football player kicks a ball from the point A with position vector (2i + j) m
on a horizontal football field. The motion of the ball is modelled as that of a particle
moving horizontally with constant velocity (5i + 8j) m s–1. Find
(a) the speed of the ball,

(b) the position vector of the ball after t seconds.

The point B on the field has position vector (10i + 7j) m.

(c) Find the time when the ball is due north of B.

At time t = 0, another player starts running due north from B and moves with constant
speed v m s–1. Given that he intercepts the ball,

d) find the value of v.

I really don't know how to do d. I tried equating I and J components but I had three unknown values for the football player; his velocity I and J and the time taken.
2. (Original post by thelion0)
8.
At time t = 0, a football player kicks a ball from the point A with position vector (2i + j) m
on a horizontal football field. The motion of the ball is modelled as that of a particle
moving horizontally with constant velocity (5i + 8j) m s–1. Find
(a) the speed of the ball,

(b) the position vector of the ball after t seconds.

The point B on the field has position vector (10i + 7j) m.

(c) Find the time when the ball is due north of B.

At time t = 0, another player starts running due north from B and moves with constant
speed v m s–1. Given that he intercepts the ball,

d) find the value of v.

I really don't know how to do d. I tried equating I and J components but I had three unknown values for the football player; his velocity I and J and the time taken.
You have found the time which the ball takes to be north of B, use it to find the distance it is, north of B at that time and then you can easily find the speed given you know the distance and time which you do.
3. (Original post by thelion0)
8.
At time t = 0, a football player kicks a ball from the point A with position vector (2i + j) m
on a horizontal football field. The motion of the ball is modelled as that of a particle
moving horizontally with constant velocity (5i + 8j) m s–1. Find
(a) the speed of the ball,

(b) the position vector of the ball after t seconds.

The point B on the field has position vector (10i + 7j) m.

(c) Find the time when the ball is due north of B.

At time t = 0, another player starts running due north from B and moves with constant
speed v m s–1. Given that he intercepts the ball
Hi there, I've been reading this post and have been wondering, how would you work out part (c) to this question? Cheers in advance!

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