# Mechanics Problem HELP!

by mikex24
Tags: mechanics
 Sci Advisor HW Helper PF Gold P: 6,049 Ok let's crank it out. P1 is (20)(2.15) = 43 and P2 is (20/2)(2.15) = 21.5, so the vert load is 64.5 N. The moment about the support is 43[(2.15/2) +.1 + 4 sin15] + 21.5[(2.15/3) + .1 + 4 sin15] = 134.9 N-m. Or, if you look at the moment at the support in the free body of the slanted member, it's 64.5(4)(sin15) + 68.1 = 134.9 N-m.....checks out OK.
 P: 70 Using the bending equations, I have a value of approx 88Pa for the induced stresses. Am I right in using the the biggest moment in the equation, which is at the ground?
 P: 70 Sorry, 44.24MPa
HW Helper
PF Gold
P: 6,049
 Quote by D44 Sorry, 44.24MPa
It's somewhere around there, I didn't calc out the numbers, but yes, max bending stress is Mc/I where M is the max moment (139 Nm) occurring at the support, which controls the overall frame structural design. The I term comes from the properties of the hollow circle, and c is its outside radius.
 P: 3 Hi, i am having the same trouble with this assignment, mainly drawing the free body diagram of each section. Not sure exactly whether to draw it as a full frame or two seperate parts. thanks
HW Helper
PF Gold
P: 6,049
 Quote by M3_CSL Hi, i am having the same trouble with this assignment, mainly drawing the free body diagram of each section. Not sure exactly whether to draw it as a full frame or two seperate parts. thanks
First draw it as a full frame to determine reactions at the fixed support at the base. Then break it up into the horizontal piece and slanted piece separately to determine forces and moments in each of those members.
 P: 3 Thanks, so for the horizontal piece, when your working out the vertical forces, how do you know whether to use the 20Mn or the 40Mn? and does it only have 2 downward forces due to the billboard and one moment force due to the slanted piece? Thank you
 P: 3 sorry i ment 20Nm and 40Nm