[填空题]
A world-class sprinter ch15pbxxyr -8: tu3jpfan burst out of the blocks to es1/n2wfvgc.u x .( ufx ;wi8cohsentially top speed abou 8.g(con/;cu fx.2ixfv1wwh ut $13.0 \; m/s$ 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? $s$