Need to know how to explain this using Newton's second law.?

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RisaRoo20

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A child on a sled comes flying over the crest of a small hill. his sled does not leave the ground (he does not catch "air") but he feels the normal force between his chest and the sled decrease as he goes over the hill. Explain this decrease using Newton's second law.
 
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.
_______________.
 
Newton's Second Law is F = ma.

Hint:
What you have to do is identify an acceleration that is present in this situation, that is not present on flat ground. Then equate that acceleration to some force between the child and the sled.
 
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