Question 2
In figure 18.9, A is the lowest point of a swing and B the highest point it reaches. What is true of the child at B?
The right answer is the one marked above.
All of its kinetic energy has become potential energy. At B the velocity is zero, and an object with no velocity has no kinetic energy at all. The whole store has been converted.
B is the moment the swing appears to hang still before starting back — the one point in the arc where no kinetic energy is left.