text: ## Essential University Physics: Volume 1 (3rd Edition)
  
  We know that $t=\sqrt{\frac{2h}{g}}$ We plug in the known values to obtain: $t=\sqrt{\frac{(2)(1.9)}{9.8}}=0.623s$ Now we can find the horizontal speed as $v=\frac{x}{t}$ We plug in the known values to obtain: $v=\frac{4.5}{0.623}=7.2\frac{m}{s}$