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 (in $ms^{–2}$ ) is (given g = 9.8 $ms^{–2}$ )