Consider an athlete of mass m doing elbow plank and knee plank exercises as shown in the figures below. In the elbow plank, the foot and upper arms are perpendicular to the ground and the longitudinal axis of the body is held at an angle e relative to horizontal as shown. In the knee plank, the longitudinal axis is held at an angle of a relative to horizonal and the upper arm is held at an angle of relative to horizonal, as shown. You can assume that there is no horizontal ground reaction force at the elbow during the elbow plank and knee plank. You know the following: m = 55 kg, 8 = 20, a = 30, = 80, A = 23 cm, B = 120 cm, C = 42 cm, E = 80 cm a E B 30 PO D