posted by Cavin .
A lunch tray is being held in one hand. The mass of the tray itself is 0.240kg, and its center of gravity is located at its geometrical center. on the tray is a 1.00 kg plate of food and a 0.300kg cup of coffee. Obtain the force T exerted by the thumb and the force F exerted by the four fingers. Both forces act perpendicular to the tray, which is being held parallel to the ground. Find T= (DOWNWARD) and F (upward)
You have to model how far apart the thumb and forefingers are. Sum moments around the thumb: forefingers, coffee, plate, and tray. The sum has to be zero, that will give you the forefingers force. Then, to get the thumb force, add forces vertical and set to zero.