In a vacuum, both the ball and the piano will hit the Earth at the same time.

Here's why:

* Gravity: In a vacuum, the only force acting on objects is gravity. Gravity pulls on all objects with the same acceleration, regardless of their mass or shape.

* No Air Resistance: Air resistance is the force that slows objects down as they fall through the air. In a vacuum, there is no air, so there is no air resistance.

Therefore, both the ball and the piano will fall at the same rate, and will reach the ground simultaneously.