1. What is the magnitude of the resultant joint reaction force with the bucket 1
ID: 1785483 • Letter: 1
Question
1. What is the magnitude of the resultant joint reaction force with the bucket 133.5 N bucket?
2. What is the calculated reduction in compressive JRF from the 267 N to the 133.5 N condition?
3. What is the shear component of the biceps muscle force when holding the bucket weighing 133.5 N at 30 degrees of elbow flexion?
You are currently working on the east coast in Portland, Maine. You see a 35 y o patient (170 cm, 65 kg), complaining of right elbow pain. She works on the docks unloading buckets of lobsters from a lobster boat. Because of the elbow pain you want to determine the elbow joint reaction force (JRF) using two different bucket loads of 267 N and 133.5 N at 30 of elbow flexion to verify that reducing the load can decrease joint reaction force. Shoulder FB Elbow Given: - Weight of the bucket (held in the hand) acts at 0.32 m from the elbow Biceps muscle inserts on the forearm segment at an angle of 30°, at a distance of 0.08 m from the elbow. COM of the forearm + hand acts at 0.186 m from the elbow. - FA-H 1 - Weight of the forearm + hand (FFA+H) is 13.701 N Assumptions Only the biceps muscle is acting to hold the position of the forearm. Upper arm is resting at the patient's side and the wrist is rigid at (disregard muscle activity at the wrist and hand)Explanation / Answer
1)
Taking moments about the elbow joint.
Fb Sin(30) *0.08 = 0.186* 13.701 + 133.5 *0.32
Fb = 1131.71 N
Let R be the JRF at the elbow joint then
Ry + Fb = 133.5 +13.701 , vertical forces
Ry = -983.8 N
Horizontal forces
Rx = Fbcos(30) = 1131.7*0.87 = 980 N
JRF = R = sqrt(9802 + 9832) = 1388.11 N
2. whe bucket is 267 N
Fb Sin(30) *0.08 = 0.186* 13.701 + 267 *0.32
Fb = 2199.7 N
Ry = 267 +13.70 - 2199.7 = -1999 N
Rx = 2199.7 *Cos(30) = 1904 N
JRF = sqrt(19992 + 19042 ) = 2760.9 N
reduction in JRF = 2760.9 - 1388.11 = 1372 N
3. Fb = 1131.7 N with bucket = 133.5 N
vertical comp = 1131.7 Sin(30) = 565.85 N
horizontal comp = 980.08 N
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