Tuesday

September 2, 2014

September 2, 2014

Posted by **Patrick** on Friday, March 28, 2014 at 6:25pm.

- Physics -
**Steve**, Friday, March 28, 2014 at 7:26pmso, the mass of the seesaw can be ignored, since it is uniformly distributed. Now for the loads and their moments. They must balance on both sides, so

14*1.4 = 39*L

Simple, no?

Actually, since I have no diagram, I can't say that the seesaw mass may be ignored. If the pivot point is not at the center, but rather at some arbitrary distance d from the left), then we have to allow for the different mass of the seesaw needing to be balanced. In that case,

20(d/4.5)+14*1.4 = 20(1 - d/4.5) + 39L

- Physics -
**Steve**, Friday, March 28, 2014 at 7:28pmOops. I just gave the mass of the seesaw on each side. That must be multiplied by the distance of its center of mass:

20(d/4.5)(d/2)+14*1.4 = 20(1 - d/4.5)((4.5-d)/2) + 39L

- Physics -
**Damon**, Friday, March 28, 2014 at 7:36pmTake moment about the left end

total mass = 20 + 14 + 39 = 73 kg

That is force up from pivot

(I am going to do force in kilograms because g will cancel everywhere.)

pivot distance from left = 1.4

Distance left to 39 kg = x

(our L is (x -1.4) )

moments about left end

14 * 0

- 73 * 1.4 up from piviot

+ 20 * 2.25 mass of plank halfway along

+ 39 * x

so

39 x + 45 = 102

x = 1.47

so L = .07 from the pivot

In other words the little kid just about balanced the plank.

**Answer this Question**

**Related Questions**

Physics?? - Two children sit 2.60 m apart on a very low-mass horizontal seesaw ...

Physics - A 437.7 N child and a 237.1 N child sit on either end of a 2.5 meter ...

physics - A fulcrum is placed under the center of a uniform 4.00m long, 3.00kg ...

Physics - A seesaw is 4 meters long and is pivoted in the middle. There is a ...

Physics - A 450.8 N child and a 101.0 N child sit on either end of a 2.2 m long ...

Physics - A 450.8 N child and a 101.0 N child sit on either end of a 2.2 m long ...

physics - Two children seat themselves on a seesaw, the one on the left has a ...

Physics - Three children are trying to balance on a seesaw, which consists of a ...

Physics - A beam of mass mb = 10.0 kg, is suspended from the ceiling by a ...

physics - An adult and a child are on a seesaw 14.5 ft long. The adult weighs ...