[填空题]
In a ballistic pendulum7kap0 bcapt ibwcw a(8) m-47y experiment, projectile 1 results in a maximum height h q:8 v/rknc x2o wrcf80bfm/*l of the pendulum equal to 2.6 cm. A second projectile causes the the pendf 8o8q*/rw:cb/rx nkm lv2f0culum to swing twice as high, $h_2=5.2\mathrm{cm}$ The second projectile was how many times faster than the first? $v_1$ = $v_2$ ([color=rgba(0, 0, 0, 0.85)]Round to three decimal places)