1. Dec 3, 2007

### B-80

A 80 kg window cleaner uses a 16 kg ladder that is 5.5 m long. He places one end on the ground 2.1 m from a wall, rests the upper end against a cracked window, and climbs the ladder. He is 2.9 m up along the ladder when the window breaks. Neglect friction between the ladder and window and assume that the base of the ladder did not slip.

(a) Find the magnitude of the force on the window from the ladder just before the window breaks.

Okay, so I know that since it is in equilibrium the sum of the torques must be 0. Therefore I can say $$\tau = 0$$ also $$\tau = \r F sin \theta$$

so $$\tau = \r F sin \theta ladder + \r F sin \theta man - \r F sin \theta window = 0$$

my book told me to set up the equation at the bottom of the ladder so I don't need to include the pavement, anyway when solving this, I get $$\tau = (1.1)(80)(9.8)sin(67.6) + (1.55)(16)(9.8)sin(67.6) - window = 0$$

with that I get 1021.29 which is wrong, any ideas?

Also there is an r in all those equations, but I don't get the formatting, so I cant put it in, but I got the radius of the guy and the ladder in there. also I once solved for 2.9 as the distance he was up the ladder in the y direction, also didn't work

(b) Find the magnitude and direction of the force on the ladder from the ground just before the window breaks.

Dind't start this yet, as I am not done part A

Last edited: Dec 3, 2007
2. Dec 3, 2007

### B-80

Bump, any help is really appriciated