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\begin{aligned} W_{\mathrm{fr}} &=F_{\mathrm{fr}} d \cos \left(180^{\circ}\right)=-F_{\mathrm{fr}} d \\ &=-(5.00 \mathrm{~N})(0.800 \mathrm{~m}) \\ &=-4.00 \mathrm{~J} \end{aligned}