Problem 6: (8 points) Muscles can only contract, so they occur in pairs. In the
ID: 2038322 • Letter: P
Question
Problem 6: (8 points) Muscles can only contract, so they occur in pairs. In the arm, the biceps muscle is a flexor- that is, it closes the limb. The triceps muscle is an extensor that opens the limb. The figure shows the forearm of a person holding a book The biceps muscle exerts a force Fa to support the weight of the forearm and the book. The triceps muscle is assumed to be relaxed. You may take the data in the figure 40kg to be accurate to three significant figures (CG-: COM) (a) Calculate the force the biceps muscle must exert to hold the forearm and its load as shown in Figure. (NS) Compare this force with the weight of the forearm plus its load. Give the answer as a factor of the combined weight. (NS) (b)Explanation / Answer
a)
net torque =0
T_biceps-T_forearm - T_book =0
FB*4*10^-2 - 2.5*16*10^-2 - 4*38*10^-2 =0
===> FB=48 N
b)
weight of the forearm and load,
W=w_forearm+w_book
w=2.5*9.8+4*9.8
w=63.7 N
==> FB/w=48/63.7
FB/w=0.75
==> FB=0.75*w