Calculating Forces in a Rotating Lunch Tray

AI Thread Summary
To solve the problem of forces acting on a rotating lunch tray, start by drawing a free body diagram that includes the tray, the food plate, and the coffee cup. Calculate the weights of the tray, plate, and cup by multiplying their masses by gravity. Apply the principles that the net force and net torque must both equal zero to establish two equations with two unknowns. This approach will allow you to solve for the forces exerted by the thumb and fingers. Understanding these concepts is crucial for accurately determining the forces involved.
tmurphy12
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Hello, I know the rules state to show work to receive help but my problem is that i don't know where to begin so i am lookign for a push in the right direction...here is the question...
A lunch tray is being held in one hand, as the figure illustrates. The mass of the tray itself is 0.200 kg, and its center of gravity is located at its geometrical center. On the tray is a 1.04-kg plate of food and a 0.248-kg cup of coffee. Obtain (a) the force exerted by the thumb and (b) the force exerted by the four fingers. Both forces act perpendicular to the tray, which is being held parallel to the ground.
http://edugen.wiley.com/edugen/courses/crs1507/art/qb/qu/c09/ch09p_16.gif
the only thing i did was multiply the masses by gravity to get their weight
again any help would be greatly appreciated.
 
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i also figure that the lever arm will be the length given in the picture...i am just confused as to how to find the force without knowing the torque
 
Draw a free body diagram for the system... with the two unknown forces they ask for. Then use two facts -- that the net force must be zero, and that the net torque must be zero. Two equations, two unknowns, so you can solve for the unknowns.
 

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