[填空题]
Grace and Henry are pla4,/b-gp9 k5cgf ximy 8syj, ghygacuq-x9z28t x1.k ix1 y5 2c 8bxc bdwci50ksing on a youth soccer field. Grace kicks a ball from $\mathrm{A}(4,3)$ with velocity vector $-5 \mathbf{i}+10 \mathbf{j}$ . At the same time, Henry kicks a ball from $\mathrm{B}(24,13)$ at 15$ \mathrm{~m} \mathrm{~s}{ }^{-1}$ in the direction $-4 \mathbf{i}+3 \mathbf{j}$ . The times and distances are measured in seconds and metres respectively.
1. Find, in terms of $\mathbf{i}$ and $\mathbf{j}$ , the :
(1) velocity vector of Henry's ball;
(2) position vector of Henry's ball after t seconds, $ t \geq 0$ .
2. Find the distance between the two balls after 2 seconds. m
3. (1) Calculate the minimum distance between the balls.
(2) Determine the position of Grace's ball when this occurs.
