Calculating the Force of the Deltoid Muscle to Raise an Arm

[Eggphys]

Homework Statement

The main muscle responsible for raising an arm is the deltoid. The deltoid muscle connects at the upper end of the shoulder, extends over the upper arm bone (humerus), and attaches near the elbow. Effectively there are three forces involved in raising the arm: (i) the force of the deltoid muscle, Fm, acting at an angle of approximately 13.2o with respect to the negative x axis, (ii) the force of gravity, Fg, acting effectively at the centre of mass of the arm located close to the elbow, and (iii) the force of the shoulder socket, Fs, acting on the humerus effectively along the x axis. Assuming the mass of the arm is 1.57 kg, calculate the magnitude of Fm in Newton.

Homework Equations

$$F=ma$$

The Attempt at a Solution

I'm not quite sure where to start. I tried using $$F_x=ma$$ and $$F_y=ma$$ to work out the net force but not getting the correct answer. Any help would be greatly appreciated. Thanks.

 

[bp_psy]

Sorry I made a mistake you can do it with just Newtons law no torques needed . Can you show your actual work force decomposition should work if you didn't do any calculation mistakes?

 

[Eggphys]

Sorry I made a mistake you can do it with just Newtons law no torques needed . Can you show your actual work force decomposition should work if you didn't do any calculation mistakes?

After going over my work abit more I see I have no clue what I am doing
Im not sure how to implement the angle into the equation or what a is in the x direction(Isnt it 0?)
Would Fy just be Fy=1.56*9.8?
Any help on where to start would be great. Thanks

 

[Eggphys]

After going over my work abit more I see I have no clue what I am doing
Im not sure how to implement the angle into the equation or what a is in the x direction(Isnt it 0?)
Would Fy just be Fy=1.56*9.8?
Any help on where to start would be great. Thanks

So i decided to come at this from another angle. First i solved for Fg,
Fg=1.57*9.8 = 15.39
Then to solve for Fm,
Fm=15.39cos 13.2 = 14.98

But the correct answer is 67.38. I am not sure where to go from here to get the correct answer. Any help would be appreciated. Thanks

 

[Eggphys]

Just bumping back to the top.