How Do You Calculate Bicep Force in a Torque Problem?

[marcia888]

7. Below is a diagram of a baseball/forearm system at rest. It is acted on by four different forces: the weight of the forearm, the weight of the baseball, the bicep force, and a force from the upper arm bone (attached at the elbow).
(Use the following values: L = 14 cm, d = 2 cm, M = 3 kg, and m = 2 kg.)

How large is the force exerted by the bicep?

Diagram:
http://www.webassign.net/userimages/ikoskelo@sfsu/bicep.jpg

I'm thinking that the torque of the forearm + the torque of the baseball combined are going to equal the negative of the torque provided by the bicep. Is this the right way to do this? And if so, I know how to figure out the torque from the baseball because I know it's distance. But how about the torque of the forearm? What is its distance? Can I just use average distance by dividing it by 2?

Thank you.

 

[marcia888]

Forget. I got it. 240.1 N

Used 1/2 distance for distance of forarm

mg L/2 + mgL = total torque down

torque up is the same. f=torque / distance , f=240.1

Thanks anyway!

 

[thepatientmental]

It seems that you are on the right track with your approach to solving this torque problem. To find the force exerted by the bicep, you can use the equation τ = Fd, where τ is the torque, F is the force, and d is the distance from the axis of rotation. In this case, the axis of rotation is at the elbow joint.

To find the torque of the forearm, you can use the equation τ = mgd, where m is the mass of the forearm and g is the gravitational acceleration. The distance d can be calculated by dividing the length of the forearm (L) by 2, as you suggested.

Once you have the torque of the forearm and the torque of the baseball, you can set them equal to the negative of the torque provided by the bicep (since they are in opposite directions). Then, you can solve for the force exerted by the bicep by rearranging the equation to F = -τ/d.

Remember to use consistent units throughout your calculations and to pay attention to the direction of the forces and torques. I hope this helps you solve the problem!