Posted by **jeff** on Monday, December 8, 2008 at 12:35am.

A bench is made of a 3 meter long plank with a mass of 12kg and 2 sawhorses(each 0.2m from an end).There are two boxes on the bench. A 15kg box is 0.8 meter from the left hand side. A second box is 0.5 m from the right hand side. What would the mass of the second box have to be for the normal force exerted by the right sawhorse to be 3 times larger than that exerter by the left sawhorse?

- physics -
**drwls**, Monday, December 8, 2008 at 2:00am
You need three equations to solve for the unknown mass M and the forces at each sawhorse, F1 and F2

One of the equations is F2 = 3 F1

Another equation can be

F1 + F2 = 4 F1 = (12 + 15 + M)g

The third equation should be a moment equation. I suggest you take it about the point of contact of the sawhorse on the right.

F1*2.6 - 15g*2.0 - 12g*1.3 - Mg*0.3 = 0

You should draw yourself a figure of the loaded plank to see where the lever arm length coefficients came from.

Now you have two equations in two unknowns, M and F1. Solve for M. The g factor can be canceled out when solving for M.

## Answer this Question

## Related Questions

- physics - A bench is made of a 3 meter long plank with a mass of 12kg and 2 ...
- physics - A cat walks along a uniform plank that is 4 m long and has a mass of 7...
- Physics - i38. tinypic .c o m /2hnxvki .gif In the experiment, the angles ...
- English Expression - Number 5, stand up. Come to the black board. Pick up a ...
- physics - A cat walks along a uniform plank that is 4.00 m long and has a mass ...
- Physics - Buffy the Vampire Slayer is buffing up her 0.53 meter long arms by ...
- Physics - Buffy the Vampire Slayer is buffing up her 0.53 meter long arms by ...
- physics/Math - Buffy the Vampire Slayer is buffing up her 0.53 meter long arms ...
- math - Jackson has a 2-meter plank of wood. He cuts two pieces of wood that are ...
- Physics - Two boxes, A and B, are connected to each end of a light vertical rope...

More Related Questions