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\begin{aligned} &\text { or } \left.\begin{array}{l} \mathrm{KE}+\mathrm{PE}=\mathrm{constant} \\ \mathrm{KE}_{\mathrm{i}}+\mathrm{PE}_{\mathrm{i}}=\mathrm{KE}_{\mathrm{f}}+\mathrm{PE}_{\mathrm{f}} \end{array}\right\} \text { (conservative forces only), } \end{aligned}