EK Physics Torque Question

[deleted699536]

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I am having trouble working through this torque question in lecture 2 of the examkrackers physics text. I understand why you can ignore the horizontal forces equation and even how to use the torque equation, but I'm not sure why the vertical forces equation results in two unknown variables: d and T.

I have:

Fup = Fdown
T = mg + m(salty)g

But I'm not sure where d comes into play in this equation. Can anyone explain this? Thanks!

 

[chemist16]

I'm not sure I understand your question. You have an equation for the torque exerted by the hippo: it's its mass times gravity times d (because torque is defined as the perpendicular force exerted dotted by the length of the lever arm). You have an equation for the torque exerted by the person: it's its mass times gravity times L. You have the torque exerted by the rope: it's the tension force that you've written down times x. The net torque is zero unless the board is rotating. So if you're given the information in the question, you can solve these equations for any variable.