[填空题]
In a ballistic pendulum experim(.1wmswd jht - fj/ew,p:sd -cent, p*crhch,x k87 srojectile 1 results in a maximum height h of the pendulum equal to 2.6 cm. A second proj*7h8c c,khrsxectile causes the the pendulum 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)
