Homework Help: physics

Posted by Physics on Monday, December 10, 2012 at 12:17am.

A hiker, who weighs 1120 N, is strolling through the woods and crosses a small horizontal bridge. The bridge is uniform, weighs 3775 N, and rests on two concrete supports, one at each end. He stops one-fifth of the way along the bridge. What is the magnitude of the force that a concrete support exerts on the bridge at each end?

physics - Jennifer, Tuesday, December 11, 2012 at 8:23pm
Let F1 and F2 be the forces on the two ends of the bridge.

The sum of the forces in the y direction is 0:

F1 + F2 - 1120 - 3775 = 0

The sum of the torques about each support is zero:

1120*(L/5) + 3775*(L/2) - F2*L = 0
Dividing by L:

1120/5 + 3775/2 - F2 = 0

Solve for F2, then solve for F1

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