If you were to drop a penny from a plane, it would accelerate due to the force of gravity at a rate of approximately 9.8 meters per second squared. As the penny falls, it would also experience air resistance, which would slow it down somewhat.
However, because a penny has a low mass and a high surface area compared to its weight, the air resistance would eventually balance out the force of gravity, causing the penny to fall at a constant speed called the terminal velocity. In the case of a penny, the terminal velocity is estimated to be around 50 miles per hour (80 kilometers per hour).
When the penny hits the ground, it would likely make a small dent or scratch, but it is unlikely to cause any significant damage or harm to people or property. Nonetheless, dropping objects from planes can be dangerous, and it is generally prohibited by law for safety reasons.