Step 1: Picture the situation.
A ball is thrown from a truck that is itself moving. We want to know what decides how far the ball lands, which is called its range.
Step 2: Understand what range means.
Range is the horizontal distance the ball covers before it lands. This distance is always measured on the ground. So whatever we use to find the range must be measured with respect to the ground.
Step 3: Add the two motions together.
The ball has two velocities to think about. One is its velocity as thrown from the truck. The other is the truck's own velocity. The ball actually moves with the sum of these, which is its velocity as seen from the ground.
Step 4: Recall the range formula.
For a projectile the range depends on its launch speed and angle measured from the ground frame: \[ R = \frac{v^2 \sin 2\theta}{g} \] Here $v$ must be the speed measured relative to the ground, not relative to the moving truck.
Step 5: Test the other choices.
Truck velocity alone is not enough, because the throw also matters. Velocity relative to the truck alone is not enough, because the truck's motion adds to it. Mass does not appear in the range formula at all, so mass cannot be the answer.
Step 6: Pick the correct factor.
Only the projectile's velocity with respect to the ground combines both effects correctly. So the range depends on the projectile velocity with respect to the ground. \[ \boxed{\text{Projectile velocity with respect to ground}} \]