A projectile is fired from the surface of the earth with a velocity of $5\;ms^{-1}$ and angle $\theta$ with the horizontal. Another projectile fired from another planet with a velocity of $3\;ms^{-1}$ at the same angle follows a trajectory which is identical with the trajectory of the projectile fired from the earth. The value of the acceleration due to gravity on the planet is : (given = $9.8 ms^{-2}$)
