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A child pulls a sled of mass $m$ up a hill that makes angle $\theta$ with the horizontal. How much work is done on the sled by gravity after the sled travels distance $L$ along the hill?

$m g L$

$-m g L$

$m g L\space sin\theta$

$-mgL\space sin\theta$

$mgL\space cos\theta$

$-mgL\space cos\theta$