Help with A and B

Experimental biophysicists use a special apparatus called "optical tweezers" to trap a micron- sized bead (indicated as the "load" in the figure below) and trace its movements as it is dragged around the cell by molecular motor proteins, like kinesin. The link below is for a video that shows a kinesin protein walking on microtubule while dragging such a load: https://www.youtube.com/watch?v=y-uuk4Pr2i8 4 In these experiments, there is a large mismatch between the size of the protein (typically few nanometers) and the load that is tethered to the motor. load Image from Physical Biology of the Cell, 2 nd edition (@Garland Science 2013) ATP motor domains ADP (ATPase) For all questions below, ignore gravity and any buoyant forces. A. Assuming the motor pulls the bead along the medium with a speed 1.0 um/s, what is the magnitude of the viscous drag force (Fv) on the bead? The viscosity of the medium, n, is 10 3 Pa . s and the bead radius is 500 nm. Express your answer in pN. B. Experiments have shown that the kinesin motor is capable of exerting forces of up to 5.2 pN. What is the largest radius (in nm) that the bead can have and still be pulled at 1.0 um