Abe and Cindy are sitting on a seesaw. Abe weighs 680 newtons and sits 1.20 meters from the pivot point on the left. Cindy weighs 450 newtons and sits 1.50 meters from the pivot point on the right. The seesaw tips counter clockwise. How far back on the seesaw would Cindy need to be in order to balance the seesaw.

Use Moment = Force\, \times\, Perpendicular\, Distance

Counter Clockwise moment = Fd = 680 * 1.2 = 816 Nm
Clockwise moment = Fd = 450 * 1.5 = 675 Nm

The resultant is 141Nm counter clockwise (816-675). Now, that is not required. But if they have to be balanced, both moments have to be equal.

Clockwise Fd = Counterclockwise Fd

680 * 1.2 = 450 * d

Where d is the distance of Cindy from the pivot point.

Solve for d, and you're done. :)

hi jerry.

I know I must sound thick to you, but given that:

680 * 1.2 = 450 * d

I still don't get how you find solve for d... lol

for a thickhead like me that's another equation to learn... lol

wish I could get my head around all this physics stuff

so...

450 * "something" = 816..

that's got to be a large decimal hasn't it??

or am I missing something

I get 680 x 1.2 = 450 * 1.8133333333

surly that can't be right can it?

god I am thick... sorry for bugging you...

its just that this is bugging me...

Sorry for late reply. I had some trouble with my internet connection...

Well, yes, that's the answer if the values you gave were the correct ones, with no typo :)

Do not be too surprised by figures with many decimals. In practice, we round up to some figures. Here for example, we will consider 1.81 m only, for I don't think one would bother to measure up to several nanometres for a see saw, lol! Once they got the balanced point, they can play with it with no trouble.