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# M2 Mechanics question Watch

1. This is the question:

I did it like this:

But for some reason in the solutions, they have S reaction force as perpendicular to the ladder? Why would the reaction be perpendicular to the ladder?

2. When a rod is resting against an edge, the rod will always rest perpendicular to that edge (this is only true because we model the ladder as a rod). Thus, the reaction force will be perpendicular to the ladder.
3. (Original post by Bealzibub)
...
At the point of contact with the sill, the sill is an edge (pointy bit), and the ladder a plane. Since the contact is smooth, the force is perpendicular to the plane - in this case the ladder.

More usually (in other questions) the end of the ladder would be against a wall, and there the wall is the plane, (and the end of the ladder the pointy bit) and hence the force is perpendicular to the wall.

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Updated: April 2, 2016
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