某人用牵引装置来锻炼关节的功能重物质量勾3千克若小腿拉绳使重物在3秒内匀速上

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  • 解(1)小腿对绳的拉力

    ∵匀速

    ∴G=F=mg

    =3kgx9.8N/kg=29.4J

    (2)W=FS

    =29.4jx0.5m

    =14.7J

    P=w/t

    =14.7J/3min =4.9w