[tariqsherwani]

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.

Ive done a b c i need help with D
thx

[ghostwalker]

(Original post by tariqsherwani)
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.

Ive done a b c i need help with D
thx

So, you know the time when the ball is due north of B.

You should be able to work out the ball's position vector at that time, and hence its distance from B

So for the other player to intercept it, you have the distance and the time it takes, hence....

[Tisabiki]

t should be equal to 1.6 when the ball is due north, so the position vector of the ball using t as 1.6 should be (10i, 13.8j)
To find the distance between B and this position you take them away, so the distance is 13.8 - 7 = 6.8j
The player must travel this 6.8 metres to meet the ball
The time taken is 1.6 seconds so 6.8/1.6 = 4.25m/s

Tis how i would attempt it anyway, apologies if it's wrong =]