1.81 Muscles and Bones: Vector Magnitude Problem

  • #1

Homework Statement


A patient in therapy has a forearm that weighs 23.0 N and that lifts a 114.0 N weight. These two forces have direction vertically downward. The only other significant forces on his forearm come from the biceps muscle (which acts perpendicularly to the forearm) and the force at the elbow. If the biceps produces a pull of 232 N when the forearm is raised 44 degrees above the horizontal, find the magnitude and direction of the force that the elbow exerts on the forearm. (The sum of the elbow force and the biceps force must balance the weight of the arm and the weight it is carrying, so their vector sum must be 137.0 N, upward.)

Homework Equations


So there's 3 vectors I think:
A: angle ?, magnitude -137N
B: angle 44 degrees, magnitude ?
C: angle 134 degrees, magnitude 232 N

The Attempt at a Solution



I don't think I have my question setup correctly, but I tried:

232sin(44) = 161.2N = x
232cos(44) = 166.9N = y

Then I use the law of cosines, but doesn't really work..if someone could walk me through the setup, I would greatly appreciate it.
 

Answers and Replies

  • #2
ideasrule
Homework Helper
2,271
0
First, draw a free-body diagram of the forearm. Label all forces, then write out Newton's second law for both the x and y directions.
 

Related Threads on 1.81 Muscles and Bones: Vector Magnitude Problem

  • Last Post
Replies
3
Views
3K
Replies
6
Views
4K
Replies
4
Views
5K
Replies
1
Views
13K
  • Last Post
Replies
4
Views
5K
  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
3
Views
18K
  • Last Post
Replies
6
Views
1K
Replies
1
Views
773
  • Last Post
Replies
5
Views
2K
Top