Joint Reaction Force: Estimate Net Moment & Force Vector in Right Knee

[Luiz]

Homework Statement

A dancer stands on his left leg (knee extended), torso and arms forwards outstretched horizontally. The right leg (knee extended) is backwards outstretched horizontally. The dancer weighs 55 kg. The length of the thigh is 35 cm, the shank 45 cm.
Draw the free body diagram.
Estimate the net joint moment and the net reaction force vector in the right knee. Neglect the foot.

Homework Equations

The Attempt at a Solution

I can estimate the net joint moment in the right knee as follows: From Dempster table: shank 0.0465 * 55kg = 2.5575 kg. The proximal segment length of the shank is 0.433 * 45cm = 19.485cm (Dempster). Now I can calculate the net moment of the right knee: 2.5575kg * 19.485cm = -49.8 Nm , as it is a clockwise direction. The joint moment must be anticlockwise so it is 49.8 Nm.

I have no idea how to calculate the joint reaction force because it is horizontal and I can not see that a ground reaction force is involved.

 

[kuruman]

I have no idea how to calculate the joint reaction force because it is horizontal and I can not see that a ground reaction force is involved.

How did you figure out that the joint force is horizontal? If gravity is the only force acting on the dancer, there is no horizontal force that might require static friction at the foot contact. Providing the free body diagram would be helpful.