A rock, 1.2 kg, was thrown into the air.  As it reaches its maximum height gravity begins to work on it.  19) What number information have you been given

To analyze the information given about the rock thrown into the air, we can break it down as follows:

1. Mass of the Rock: The rock has a mass of $1.2 \, \text{kg}$. This is a fundamental property that will be important for calculating gravitational force and potential energy.

2. Action of Gravity: It is mentioned that as the rock reaches its maximum height, gravity begins to act on it. This indicates that the rock is being influenced by gravitational acceleration, which is approximately $9.81 \, \text{m/s}^2$ on Earth.

3. Maximum Height: Although the exact maximum height isn't provided, it is implied that the rock has reached a point where its vertical velocity is zero before descending due to gravity.

In summary, the primary pieces of information we have are the mass of the rock and the acknowledgment of gravitational forces acting upon it.