Question

Example 8.6 A Weighted Forearm Goal Apply the equilibrium conditions to the human body. Humerus Biceps Problem AW = 51.5 N (12 lb) weight is held in a person's hand with the forearm horizontal, as in Figure 8.11. The biceps muscle is attached d = 0.0296 m from the joint, and the I- weight is I = 0.346 m from the joint. (b) Find the upward force F exerted by Figure 8.11 (a) A weight held with the the biceps on the forearm (the ulna) forearm horizontal. (b) The mechanical and the downward force R exerted by model for the system. the humerus on the forearm, acting at the joint. Neglect the weight of the forearm. Strategy The forces acting on the forearm are equivalent to those acting on a bar of length 0.346 m, as shown in Figure 8.11b. Choose the usual x- and y- coordinates as shown and the axis O on the left end. (This completes Steps 1 and 2.) Use the conditions of equilibrium to generate equations for the unknowns, and solve. Solution Apply the second condition for equilibrium (step 3). St; = TR+TF +TBB = 0 R(0) + F(0.0296 m) - (51.5 N)(0.346 m) = 0 N F = lb Apply the first condition for equilibrium (step 4). F = F + R - 51.5 N = 0 R = F - 51.5 N = 602 N - 51.5 N R = N R = lb Exercise 8.6 Hints: Getting Started I'm Stuck Suppose you wanted to limit the force acting on your joint to a maximum value of 8.14 x 102 N. (a) Under these circumstances, what maximum weight would you attempt to lift? Fmax = N (b) What force would your biceps apply while lifting this weight? Fbiceps = N

Answer 1

Balance the forces in vertical and balance the moments about the end.

DATE PAGE No Sol Example W=51SN d = 0.0296m 1=0.346m W Apply second condition for equilibrium (Balance moment about lef -Vend I E Torque o +FdcWP = 0 EX0.0 29.6 -51.5*0.346 co - 601.99 F = 602 N. It=135.33 lbl Apply forst condition - F-R-WEO R = F-w R = 602-51.5 R = 550.50 - 123.76

Epertise 8.6 DATE PAGE NO. Farma 8.14 X102N = 814 | Мах и со aching on th Apply and condehou Rlo) + Ed - When l zo 81440,0296. Wmax 8.0.346=0 H Max weight Wonex = 69. 64 N v l to letu torceps is R Apply condition I o f - Wuer - R = R- f - Wimax . R = 814-6964 LR = 744.36 N o