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Two kids create a makeshift seesaw by setting a 4-m long uniform plank on a saw horse?
The saw horse is 0.5 m to the left of the center of mass of the plank. The child of mass m1 = 48 kg sits at the left end of the plank. The child of mass m2 = 35 kg sits 1 m to the right of the center of mass of the plank. What is the mass of the plank?
Setting aside the fact that this is obviously your homework...
This problem has several faults.
-It doesn't specify that the plank is balanced in said state. (but we can assume that)
-The child on the right side is sitting "1m to the right of the 'center of mass' of the plank" Is 'center of mass' referring to the 'center of gravity'? The mass of the plank should remain constant no matter where the fulcrum or children are sitting. So i guess we're assuming that the 'center of mass' occurs at 2m down the board and the child is sitting 1m from the center and 1m from the end? Wouldn't it be easier to say 'the child on the right is sitting 1m from the right end of the board"? Correct your teacher on this.
LeftMassOfBoard + LeftChildsLeaveredForce = RightMassOfBoard + RightChildsLeaveredForce
3.5x + 48(3.5) = 4.5x + 35(1)
Solve for X. That gives you the Mass per meter of the board. Then multiply by 4 cause the board is 4 meters long and you should have your answer.
Pushups / Plank Jacks 2 (Bicep Flexing @ end) 4/22/2010