# Homework Help: See Saw and Pivot Location

1. Nov 6, 2008

### uno

1. Harry, who weighs 360 N, and 170 N Gretchen are about to play on a 8.00 m long seesaw. He sits at one end and she at the other. Where should the pivot be located if they are to be balanced?

2. F1R1 = F2 R2; F1=360N F2 = 170 N. The problem gives the total length, and I know I need to find out the distance of Gretchen first, but I can't seem to figure it out. I have also used the formula (M1*g)R1 = (M2*g)R2, but again I'm not sure how to figure out the distance of Gretchen.

3. I tried to use this formula to figure out Gretchen's distance. To = r (mass).

2. Nov 6, 2008

### uno

I forgot to include:

They are looking for the distance in meters from Harry.

Thanks

3. Nov 6, 2008

### LowlyPion

Let L be the length from Harry. Then if it balances doesn't

360N * L = 170N * (8 - L) ?

4. Nov 6, 2008

### uno

In order to figure out the distance of Harry, don't we need to figure out the distance of Gretchen? I'm not sure what valut to put in for L where you have 8-L.

5. Nov 6, 2008

### mheslep

Uno: You have two unknowns R1, R2, so you require two equations for a solution:
Balance the torque moments:
F1*R1 = F2*R2,
and
R1+R2=8

Then solve for R1 or R2:
R1=(F2/(F1+F2)) * 8, the pivot is 2.57M from the larger force. Note the three significant figures in the answer. You were given 3 sig figs in the problem, be sure to include 3 in your answer or a tough TA/Prof might ding you.