Answer
$v_{_x} = 53.78m/s$
Work Step by Step
$K_i+U_i = K_f+U_f$
$K_i+U_i -U_f = K_f$
$ K_f = K_i+U_i -U_f$
$K_i$ and $U_i $ are already given so lets find $U_f:$
$U_f = mgh$
$=0.55kg \times 9.8m/s^2 \times 140m$
$= 754.6J$
$ K_f = K_i+U_i -U_f$
$ K_f = 1550J +0J -754.6J$
$ K_f = 795.4$
Calculating horizontal velocity from $K_f$:
$ K_f =\frac{1}{2}mv_{_x}^2 $
$v_{_x} = \sqrt {\frac{2K_f}{m}}$
$v_{_x} = \sqrt {\frac{2\times795.4J}{0.55kg}}$
$v_{_x} = 53.78m/s$
