Review Torque - Irion County ISD

Torque with
force applied
at 90o:
800 N
x 0.175 m
140 N•m
Physics Bell Ringer 12-2-13
What is the torque about the shoulder if
the arm is held in an abducted position at
60 degrees from the body in the frontal
plane while holding a 10 kg dumbbell?
Assume that the mass of the arm is 6 kg,
its center of mass is located 38 cm from
the shoulder joint center, and the arm's
total length is 80 cm.s
Draw a vector diagram and show
Physics – Final Bell Ringer, Torque
A hand exerts an upward force of 90 N on a scale at 32 cm from the joint center at
the elbow. The triceps attach to the ulna at a 90° angle, and at a distance of 3 cm
from the joint center. The weight of the forearm and the hand is 40 N with the
forearm/hand center of gravity located 17 cm from the elbow joint center.
Considering these conditions, how much force is being exerted by the triceps?
(Remember that you are interested in the forces acting on the forearm system.)
(answer: 733.3 N)
Physics – Final Bell Ringer, Torque: Solution
90 N
40 N
3 cm
32 cm
17 cm
Let CCW direction be positive and CW be negative :
(40 N)(0.17 M) ‒ (90 N)(0.32 m) = ‒ (0.03 m) X
X = 733 N
Thursday, Physics Problem
A charter flight company is hired to carry a load of freight using their Cessna 183 from Anchorage to
Nome, AK. The aircraft specifications, along with the pilot data are given below. Where should the load
of freight be placed in relaton to the “datum” in order to carry the maximum allowable weight? Assume
the plane is carrying a full load of fuel. Notes:
1. “Dry weight” means the airplane’s weight without any fuel, personnel or freight on board.
2. The center of mass in this case serves as the axis of rotation.
Max allow.
freight =
2950 lb.
Pilot =
200 lb.
Freight =
746 lb.
‒ 1700 lb.
‒ 56x9 lb.
‒ 200 lb.
546 lb.
(200)(44-22) = 546d
d = 8 in. from CM
From datum, d = 8+44 = 52 in.

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