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# Quick M2 question watch

1. So in this question, two rods are connected by a hinge at B by there is no Y or X force. But the hinge at A does.

However, this question:

There is a Y and X force at the hinge at B. I thought two rods connected to each other with a hinge, have net 0 resultant force because they both cancel each other out and act as internal forces?
2. (Original post by Bealzibub)
So in this question, two rods are connected by a hinge at B by there is no Y or X force. But the hinge at A does.

However, this question:

There is a Y and X force at the hinge at B. I thought two rods connected to each other with a hinge, have net 0 resultant force because they both cancel each other out and act as internal forces?
I may be interpreting the latter system incorrectly*, but the fact that it refers to AC as "the rod" seems to suggest that the points A, B and C must remain collinear throughout the motion i.e. the two sections AB and BC are not free to rotate independently of one another via the hinge (as is the case in the first system you mention, in which the two sections are connected only by the hinge and are independent otherwise). Instead, the entire rod rigidly rotates about B and therefore a force is exerted by the entire rod on the hinge at B.

*The only reason I am unsure is because the question chose to use the word "hinge" as opposed to "pivot". I'm more than prepared to be corrected!

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Updated: May 18, 2016
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