For the purposes of this question, we will make a simplifying assumption that the only muscle that participates in lifting the arm laterally in abduction is the deltoid muscle. Assume that the insertion point for the deltoid on the humerus is 10 cm from the glenohumeral joint and line of action for this muscle (and all of its components together) is 10° from horizontal when the arm is at 90° abduction (straight to the side). You can assume that person has a body mass of 80 kg. The arm is 55 cm long, and the mass of the arm is approximately 5% of total body weight. Assume that the mass of the arm acts at about 40% of the total length of the arm (on the more proximal side). 0 = 10° 10 cm 55 cm Figure 1: Position and dimensions of the arm in abduction. A) Using this information, calculate the load (N) on the glenohumeral joint when there is no weight in the hand. What is the percent body weight of this load? B) Repeat the calculation when the hand is holding a 2 kg mass. Assume that 55 cm is the distance from the glenohumeral joint to the palm of the hand (and the weight).

You are trying to evaluate the amount of force a worker must exert and see if implementing an assistive device would help reduce injury for the work. Pictured below, the worker and the job you are assessing. You are interested in the shoulder joint for this problem. ● The drill weighs 3.1 kg and is 80 cm away (horizontal distance) from the shoulder joint ● The worker's arm weighs 17 lbs from the shoulder to the fingers. The center of mass of this weight is 40cm from the shoulder joint. Show the units. 1. Draw a FBD for the right arm only. a. Assume the drill is not touching the wall. b. Assume the worker is not supporting themselves on anything c. Assume the deltoid muscle is holding up the drill. The deltoid muscle is pointing towards the shoulder joint and runs parallel to the arm but 2 cm above the shoulder joint Also, calculate the deltoid muscle force. Is the muscle for pointing towards the shoulder or away from the shoulder?

B7

The tune-up specifications of a car call for the spark plugs to be tightened to a torque of 38 N ⋅ m. You plan to tighten the plugs by pulling on the end of a 25-cmlong wrench. Because of the cramped space under the hood, you’ll need to pull at an angle of 120° with respect to the wrench shaft. With what force must you pull?