Let Fn = normal force
When the sled is moving on level ground then
Fn = mg (on level ground)------(1)
The crest of a hill is rounded. Therefore the child experiences downward centripetal acceleration.
Let centripetal acceleration = a
The two forces acting on the child are
1. Weight mg downward
2. Fn upward
Acceleration = a (downward)
Therefore mg - Fn = ma
Fn = mg - ma (on crest)-----------(2)
From (1) and (2),
Fn on crest is less than that on level ground.
