Answer: Electromagnetism and sound
Explanation:
The moment of A about B is given by the formula

where M is the moment, F is the force acting perpandicular to the axis of rotation about B by A, and d is the horizontal distance of A from B along the axis of rotation.
Now

(a) At X,

(b) At 0.5m from X,

(c) At Y,

where negative sign indicates clockwise rotation of the child about Z.
(d) At Z,

Answer:
because the moon returns to the same place on the sky once every siderial period, but the sun is also moving on the sky.
Explanation:
Hope that helps!