The units of force, velocity and energy are 100 dyne, 10 ${cm s }^{ -1 }$ and 500 erg respectively. The units of mass, length and time are:

Force $= 100 dyne= M^{1}L^{1}T^{-2}$

$velocity = 10 \dfrac{cm}{s}=LT^{-1}$

$Energy = 500 erg =M^{1}L^{2}T^{-2}\Rightarrow \dfrac{energy}{force}=L^{1}=\dfrac{500}{100}=5cm$

$\Rightarrow \dfrac{energy}{(velocity)^{2}}=M^{1}=\dfrac{500}{(10)^{2}} =5gm \Rightarrow T=0.5\ sec$