Q1.
She wondered — does the Sun move in the sky? Or does the Earth move?
Answer
The Earth moves. The Sun only appears to move across the sky because we watch it from an Earth that is spinning.
Rashmika saw two things and could not fit them together. She saw the coconut-tree shadows change length through the day, which made her think the Sun travels across the sky. She had also learnt in Grade 6 that the Earth goes around the Sun. Both observations are real; the missing piece is the Earth's rotation — its spin on its own axis, once in about 24 hours.
Why it happens: when you sit on a merry-go-round turning anti-clockwise, the trees around you seem to swing past in the clockwise direction. You are moving, not the trees. In exactly the same way, the Earth turns from West to East, so the Sun appears to come up in the East, cross the sky and go down in the West. That changing direction of the Sun is what makes shadows long in the morning, short near noon, and long again by evening.
Two different motions: the Earth rotates on its axis (about 24 hours — this gives day and night) and it revolves around the Sun (about 365 days and 6 hours — this gives the year and, with the tilt, the seasons). Rashmika had remembered the second one and forgotten the first.