Question

3. A person is wearing a weight boot (150 N) and doing exercises to strengthen the knee extensor muscles. The center of mass of the weight boot is 0.35 meters from the center of rotation of the knee. The person's foot + shank has a weight of 40 N and its center of mass is 0.2 meters from the center of rotation of the knee. These distances are along the length of the shank.

- When the shank is perpendicular to the ground, what is the total torque about the knee? (Be sure to use a free-body diagram.)

b. When the shank is held at a position where it is 20° below the horizontal (foot is lower than knee), what is the torque about the knee? (Be sure to use a free-body diagram. Note that the moment arm of the weight boot about the knee changes with knee angle.)

- If the quadriceps muscle group has a moment arm of 0.025 m, what is the muscle force needed to hold the shank at 20° below the horizontal?

Answer #1

A 82 kg individual is in a seated positio n on a machine that
tests knee extension strength . The calf length is 0.44 m , the c
alf/foot mass is 5.9 % of the body mass, t he calf/foot center of
mass is 59 % of the calf length from the knee join t, and t he
calf/foot mo ment of iner tia about the knee joint is 0.36 kgm 2 .
The quadriceps moment arm is 0.04 3...

An 80 kg individual is in a seated position on a machine that
tests knee extension strength. The calf length is 0.440 m,
calf/foot mass is 5.8% of the body mass, calf/foot center of mass
is 53% of the calf length from the knee joint, and calf/foot moment
of inertia about the knee joint is 0.350 kgm2. The quadriceps
moment arm is 0.040 m. The machine’s padding contacts the calf at a
constant moment arm (does not change with knee...

Determine the amount of torque that is needed to hold up a
weight with the arm at shoulder level. Draw a free body diagram to
represent it. Assume the following and show all work:
Weight that is being held= 12 lbs
Center of mass of the limb = 26 cm from shoulder joint
Weight of limb= 8.5 lbs
Angle of insertion of the deltoid is 15 degrees. Moment arm is 3
cm.
Length of the limb = 65 cm
Weight...

A) A man holds a 185-N ball in his hand, with the forearm
horizontal (see the figure). He can support the ball in this
position because of the flexor muscle force , which is applied
perpendicular to the forearm. The forearm weighs 18.2 N and has a
center of gravity as indicated. Find (a) the magnitude of and the
(b) magnitude and (c) direction (as a positive angle
counterclockwise from horizontal) of the force applied by the upper
arm bone...

Uniform Copper Cone
Height: 3cm
Diameter: 2cm
Center of Mass: H/4
Moment of Inertia: 8.445 x 10-7
We are going to discuss spinning the cone like a top.
Assume that the cone is place on its tip and is perfectly vertical
and initially at rest. It is grabbed by two fingers at the very top
on both sides that exert the same constant 5 N frictional force to
the base of the cone for 0.1 seconds. The normal forces from...

1. A person pushes on a doorknob with a force of 5.00 N
perpendicular to the surface of the door. The doorknob is located
0.800 m from the axis of the hinges of the door. The door begins to
rotate with an angular acceleration of 2.00 rad/s2. What
is the moment of inertia of the door about hinges?
Select one:
a. 6.50 kg.m2
b. 2.50 kg.m2
c. 12.5 kg.m2
d. 2.00 kg.m2
2. A dumbbell has a connecting bar of...

2. A 100 cm rod is free to pivot about one end, and a 50 N force
is applied at the other end at an angle 20 degree to the
horizontal.
(i) Calculate the lever arm of the rod.
(ii) Calculate the torque about the pivot point.
3. Joe weighing 500 N sits 0.5 m to the left of center of the
seesaw 2 m long. Liz sits at the end on the opposite side of a
seesaw of mass...

A spool of thread has rolled under the bed! Fortunately, you get
the free end of it
thread. The moment of inertia of a homogeneous, full cylinder
about
Its axis of symmetry is: ? = (1/2) ?? ^ 2. The moment of inertia of
the whole spin about the axis of rotation is: ???? = 15?? ^ 2. The
friction between the reel and the floor is ?? = 0.25
(static) and ?? = 0.2 (dynamic).
You start pulling the thread...

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