2. جسمان يتحركان على سطح أفقي غير أملس

2.2. شد الخيط بين جسمين مع الاحتكاك

نستخدم تعبير التوتر الذي وجدناه في القسم السابق:

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نعوّض تعبير التسارع الذي وجدناه:

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