**Sample Problem**

A ladder of length L = 12 m and mass m = 45 kg leans against a slick (friction less) wall. Its upper end is at height h = 9.3 m above the pavement on which the lower end rests (the pavement is not friction less). The ladder’s center of mass is L/3 from the lower end. A firefighter of mass M = 72 kg climbs the ladder until her center of mass is L/2 from the lower end. What then are the magnitudes of the forces on the ladder from the wall and the pavement?

SOLUTION: First. we choose our system as being the firefighter and ladder, together. and then we draw the free-body diagram. The firefighter is represented.

The balancing equations apply to it. Let us start with. To choose an axis about which to calculate the , note that we have unknown)at the two ends of the ladder.

To find the moment r i of we draw a line of action through that vector . Then r i is the perpendicular distance between 0 and the line of action.Extends along the y axis and is equal to the height.

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