Final answer:
The problem requires applying the principles of static equilibrium to calculate the force of the flexor muscle and the force at the elbow joint when a man holds a ball with his forearm horizontal. The solution involves finding the torque caused by the ball's weight and the weight of the forearm to determine the muscle force, and then calculating the resultant net force at the elbow joint.
The correct option is nt given.
Step-by-step explanation:
The student is tasked with determining the forces acting on a forearm when holding a ball. From the information provided, we have a 190-N ball and the weight of the forearm at 20.9 N.
To calculate the force exerted by the muscles and the elbow joint, we must apply the principles of static equilibrium, where the sum of all torques and forces must equal zero since the forearm is not moving. The muscle force must provide a counteracting torque to the weight of the ball and the weight of the forearm.
Force of the flexor muscle: To prevent the forearm from rotating downwards, the flexor muscle must exert a torque equal and opposite to the torque exerted by the weight of the ball and the weight of the forearm.
Force at the elbow joint: This is the net force needed at the elbow to keep the system in equilibrium. It must counter the weight of the ball and the forearm, plus any additional force exerted by the muscle.
The direction of the force: This is the angle at which the force applied by the upper arm bone to the forearm acts, measured counterclockwise from horizontal.
The correct answer would involve solving for the force of the flexor muscle first and then finding the resultant force at the elbow joint, taking into account both the magnitude and direction.
The correct option is nt given.