Question

True or False Statements for Rigid Bodies

Answer 1

i. A roller touching a surface can exert a force perpendicular to the surface.
ii. A fixed support at one end of a beam can only exert a force on the beam.
iii. In a typical free-body diagram, the weight of an object acts at its centre of gravity.
iv. For a three-force member to be in equilibrium, the three forces must sum to zero and their moments about any point must sum to zero.
v. A single smooth pin connected to a body cannot exert a moment on the body parallel to the pin.
vi. If a body is subjected to more unknown reactions than available equations of equilibrium, then the problem cannot be solved completetly.
vii. Couple moments can be placed anywhere on a free-body diagram.

Answer 2

What do you think?

iii and iv at least are true.

Answer 3

@Vincent-Lyon.Fr
I believe 1 is true , 2 is false ,3 is true, 4 is true , 5 is false , 6 is false and 7 is true

Answer 4

The only one where our answers would differ is number 6. Have you ever heard of degrees of freedom? Or even the Gibbs Phase rule by chance?

Answer 5

If there are more unknown reactions forces then there are equations, then the problem is not solvable using simply mass/force balances. You CAN however use alternate methods to solve it.

Answer 6

Have you heard of kinematics, constitutive behavior, equilibrium, and compatibility methods?

Answer 7

Ya i've heard of Gibbs Phase rule and I heard of all the methods you're saying

Answer 8

This is the way you would solve a problem when the degrees of freedom doesn't equal zero. You basically add equations so that DF=0. SO for #6 i would say that the statement is true generally, but I can see why you would put false. So that one can go either way i would say...

Answer 9

Ya but I've inputed both thoughts True and False and it still seems I am incorrect with this question . Meaning I am wrong with another statement

Answer 10

I am a chemE but from my vague memory of statics/mechanics of materials, i think that a pin cannot translate a moment. That is why pins are used. So 6 might be true.

Answer 11

5 might be true i mean haha

Answer 12

I got it right seems all are true except for the case of
ii. A fixed support at one end of a beam can only exert a force on the beam.
Thanks for helping me with this. I work better when someone is thinking it with me

Answer 13

Sure thing bud

Answer 14

Quote: "... all are true except for the case of ii."

That's also my opinion.