Answer:
The time taken by the projectile to fall to the ground is 1 second.
Step-by-step explanation:
It is given that,
Acceleration due to gravity on the planet Zorb,

Angle of projectile is 30 degrees
Initial velocity of the projectile, u = 10 m/s
Let t is the time taken for the projectile to fall to the ground. Using second equation of motion to find it

When it fall to the ground, h = 0 and a = -g

On solving the above quadratic equation, we get the value of t as,
t = 1 second
So, the time taken for the projectile to fall to the ground is 1 second. Hence, this is the required solution.