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, $g = 9.8$ m/s$^2$)