For this case we have that by definition, the potential energy of an object is given by:
![U = mgh](https://img.qammunity.org/2020/formulas/physics/middle-school/8dn7weh0u3z0x50mdn9c63otp1p54f4u28.png)
Where,
- m: mass of the object
- g: acceleration of gravity
- h: height of the object
Substituting values we have:
![U = (2) (9.8) (4)\\U = 78.4 J](https://img.qammunity.org/2020/formulas/physics/high-school/625e9jv4gqgk1bjt1elbfdp450pw1rwwxm.png)
Answer:
Relative to the ground its potential energy is:
![U = 78.4 J](https://img.qammunity.org/2020/formulas/physics/high-school/hjoeauh0wxiqitmp3h9e04rvtsmy120i72.png)