[填空题]
A world-class sprinter can burst out of thec5* u7f 2y+barzgjgw8 fg40*9dxhd aa blocks to essentially top speed aboud9gda 0xhf* a4t $13.0 \; m/s$ in the first 18.0 m of the race. What is the average acceleration of this sprinter? $m/s^2$ and how long does it take her to reach that speed? $s$