7.38.Model:Assume the particle model for 1,m2,mand 3,mand the model of kinetic friction. Assume the ropes to be massless, and the pulleys to be frictionless and massless. Visualize:Solve:Newton’s second law for 1mis 1G111().TF ma−=Newton’s second law for 2mis () () ( )( )22on2G220 N2.0 kg9.8 m/s19.6 NmyFnFn=−= ⇒==∑2on 2k2222k212(2.0kg)mxFTfTmaTnTaμ=− −=⇒−∑Newton’s second law for 3mis ( )3on2G333myFma=∑Since 123, , and mmmmove together, 3.aa aa==− =The equations for the three masses thus become
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