Thank you for reporting, we will resolve it shortly
Q.
A spring gun of spring constant $ 90\, N/cm $ is compressed $ 12 \,cm $ by a ball of mass $ 16\, g $ . If the trigger is pulled, the velocity of the ball is
Kinetic energy of ball = potential energy of spring ie,
$ \frac{1}{2}m{{v}^{2}}=\frac{1}{2}k{{x}^{2}} $
$ \therefore $ $ 16\times {{10}^{-3}}\times {{v}^{2}}=\frac{90}{{{10}^{-2}}}\times {{(12\times {{10}^{-2}})}^{2}} $
Or $ {{v}^{2}}=\frac{90\times 144\times {{10}^{-4}}}{{{10}^{-2}}\times 16\times {{10}^{-3}}} $
Or $ v=90\,m{{s}^{-1}} $