If an object's mechanical energy is equal to its potential energy, how much kinetic energy does it have? how do you know?

Answer 1

Since mechanical energy is the sum of kinetic and potential energy, the answer to your question is zero.

E(mech) = E(pot) + E(kin)
E(kin) = E(mech)- E(pot)= 0, in this case

Answer 2

this sucks