(1) y = ax 2+bx+c can be obtained by parabola function, and (0,0), (20,40) and (30,0) can be known from the graph/kloc-0, and the coordinates of the above three points are brought into the relationship:

0=c

40=a×400+b×20+c

0=a×900+b×30+c

A=- 1/5, b=6 and c=0 can be obtained by solving the equation.

The functional relationship between y 1 and t is y 1 =- 1/5x 2+6x, 0≤t≤30.

The relationship between y2 and t can be obtained from fig. 2 as follows:

╭2x (0≤x