the isolated system

[aaronb]

1. The problem statement, all variables and given/known data


A 180 N child is in a swing that is attached to ropes 1.80 m long. Find the gravitational potential energy of the child-Earth system relative to the child's lowest position at the following times.

(a) when the ropes are horizontal

2. Relevant equations

Kf+Ugf=Ki+U[SUB]gi[SUB]

3. The attempt at a solution
I am confused on how to set up the equation

[enricfemi]

it just ask you how to find the potential which can be known by the weight of the child and the length of the ropes.

it doesn't tell you the velocity while the ropes are horizontal, so you cant set up the energy-conservation equation.