Question

Let's begin by determining the equilibrium position of a seesaw pivot. You and a friend play on a seesaw.Your mass is____
90 kg, and your friend’s mass is 60 kg. The seesaw board is 3.0 m long and has negligible mass. Where should the pivot be placed so that the seesaw will balance when you sit on the left end and your friend sits on the right end?

Answer 1

Answer:

1.2 m from the left end

Explanation:

$M$ = mass of the person = 90 kg

$m$  = mass of friend = 60 kg

$r$  = distance of pivot from the person or from the left end

$L$  = length of the seesaw board = 3.0 m

$s$  = distance of pivot from the friend or from right end = L - r = 3 - r

Using equilibrium of torque about the pivot

$M g r = m g s\\(90) r = (60) (3 - r)\\90 r = 180 - 60 r\\90 r + 60 r = 180 \\150 r = 180 \\r = 1.2$