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Physics equilibrium and balance?
I really don't understand what STEPS to follow to do this problem.
We have a plank of length 6.0 m, which is held by two sawhorses at a distance 1.5 m form each other and 0.75 (each) from the centre of the plank. On the left end of said plank there is a mass of 90 kg, while on the right end there is a man. How massive should this man be in order for the system to be balanced?
Now, my book says that "in order for the system to be balanced the centre of gravity should coincide with the right sawhorse". Why??
Thanks
when I have two sawhorses, where is the pivot?
what if I choose the lef sawhorse?
and actually the answer should be m= 30 kg
3 Answers
- PearlsawmeLv 79 years agoFavorite Answer
For balancing there is no need of the left sawhorse.
Imagine that there is no left sawhorse.
With a single right sawhorse the system can be balanced.
How? If he center of gravity of the whole system lies on the right sawhorse.
This is what your book says.
Taking moment about the right sawhorse ,
90 kg * distance of the right sawhorse from him must be equal to W kg * distance of the right side man to the right sawhorse.
distance of the right sawhorse from the left end is 3 + 0.75 = 3.75 m ( or you find it in your way )
distance of the right sawhorse from the right end is 3- 0.75 = .2.25 m ( or you find it in your way )
W =90* 3.75 / 2.25 = 150 kg
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- 9 years ago
you just need to balance the torques about the Center of mass and also equate the forces so that the body is in Equilibrium.
