Problem

A cat walks along a uniform plank that is 5.00 m long and has a mass of 9.00 kg.  The plank is supported by two sawhorses, one 0.500 m from the left end of the board and the other 1.75 m from the right.  When the cat reaches the right end, the plank just begins to tip.

a)  Draw a FBD showing all the forces on the plank.

b)  Write down the torques due to all four forces, choosing the axis of rotation to be at the point of contact between the right sawhorse and the plank.  (Note that the torque due to F₁ is zero because F₁ is zero and that the torque due to F₂ is zero because r₂ is zero.)

c)  Write down the torque equilibrium equation and solve the equation for the mass of the cat.

d)  Write down the force equilibrium equation and solve for the force F₂ on the second sawhorse.