A uniform disk of mass m = 2.4 kg and radius R = 25 cm can rotate about an axle through its center. Four forces are acting on it
as shown in the figure. Their magnitudes are F1 = 8.5 N, F2 = 1.5 N, F3 = 6.5 N and F4 = 6.5 N. F2 and F4 act a distance d = 3.5 cm from the center of mass. These forces are all in the plane of the disk. Write an expression of the magnitude of the torque due to the force F3
Torque is the cross product of the radius vector and the force vector.
τ = r × F
In other words, the magnitude of the torque is equal to the magnitude of the radius times the magnitude of the force times the sine of the angle between them.
τ = rF sin θ
Since F₃ is parallel to the radius vector, θ = 0, so τ = 0.
