Four forces are applied to a wheel of radius 20 cm as shown in Fig. The net torque produced by the forces about O is ___Nm

Magnitude of torque = Fr sin θ where θ is the angle between the force vector and the radius vector. The torques are (see Fig)τ1=8N×0.2m×sin⁡30∘=0.8Nm (clockwise) τ2=4N×0.2m×sin⁡90∘=0.8Nm (anticlockwise) τ3=9N×0.2m×sin⁡90∘=1.8Nm (clockwise) τ4=6N×0.2m×sin⁡0∘=0∴Net torque= + 0.8 Nm - 0.8 Nm + 1.8 Nm + 0 = 1.8 Nm clockwise.