[问答题]
A child on a sled comes flying over the crest of a small hill, as shown v kst0 raazafj(4 b4,,im4z( nlvn2fta70 qgo ob/+mv* n Fig. 5–31. His sled does not leavezl/* 4vm 2 +q07(n tmbvnogoaf the ground (he does not achieve “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.
