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The initial speed is 0 m/s

We let go of the rope

What is the system's kinetic energy when the little block is at 15 cm from the ground?

What's wrong with my work?

[tex]E_{t}=E_{P}+E_{F}+E_{K}\Rightarrow E_{K}=E_{t}-E_{P}-E_{F}[/tex]

where Et is total energy, Ep is potential energy, Ef is friction energy and Ek is kinetic energy.

[tex]E_{K}=0.75*9.81*0.45-0.75*9.81*0.15-0.1*2.5*9.81=-2.4[/tex]

The answer is 1.47, but i get -2.4

What to do?

Thank you

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# Homework Help: Energy conservation Law

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