机械能量怎么求?我在国外上学,what is the total mechanical energy when a shopping trolley is pushed 10m with a force of 50N?Frictional force of 7.8N act on the shopping trolley.

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机械能量怎么求?我在国外上学,what is the total mechanical energy when a shopping trolley is pushed 10m with a force of 50N?Frictional force of 7.8N act on the shopping trolley.
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机械能量怎么求?我在国外上学,what is the total mechanical energy when a shopping trolley is pushed 10m with a force of 50N?Frictional force of 7.8N act on the shopping trolley.
机械能量怎么求?
我在国外上学,
what is the total mechanical energy when a shopping trolley is pushed 10m with a force of 50N?Frictional force of 7.8N act on the shopping trolley.

机械能量怎么求?我在国外上学,what is the total mechanical energy when a shopping trolley is pushed 10m with a force of 50N?Frictional force of 7.8N act on the shopping trolley.
推力50N 摩擦力7.8N 所以合外力是42.2N 那么做的功全部转换成为动能 (题目中没有提到推车是不是在坡面上滑动 所以不考虑重力势能的变化),即全部变为机械能
所以机械能的增量=动能增量=合外力*力方向上位移=42.2*10=422J

W=F*S=10*(50-7.8)=422