Answer
$1.4\times 10^{-4}Kg$
Work Step by Step
We can find the value of $m$ as follows:
$E=\frac{1}{2}mv_f^2-\frac{1}{2}mv_i^2$
We plug in the known values to obtain:
$E=\frac{1}{2}(5.5Kg)[(5.5m/s)^2-(6.9m/s^2)^2]$
$E=-47.74J$
We know that
$E=mL_f$
This can be rearranged as:
$m=\frac{E}{L_f}$
We plug in the known values to obtain:
$m=\frac{47.74J}{33.5\times 10^4J/Kg}$
$m=1.4\times 10^{-4}Kg$
