# A Lunch Tray

1. Oct 26, 2009

### CaptFormal

1. The problem statement, all variables and given/known data

The mass of the tray itself is 0.187 kg, and its center of gravity is located at its geometrical center. On the tray is a 1.31 kg plate of food and a 0.300 kg cup of coffee. Assume L1 = 0.0610 m, L2 = 0.130 m, L3 = 0.224 m, L4 = 0.365 m and L5 = 0.387 m. Obtain the magnitude of the force T exerted by the thumb. This force acts perpendicular to the tray, which is being held parallel to the ground.

http://schubert.tmcc.edu/enc/47/9987abe8e7e44d5087aff777d122d591341673a3566037a0f448fca2c8a436593db5631f9eac0f94694865573949bce715d4c2ba0fcc1555ce73cdf70aa0bc55.gif

2. Relevant equations

3. The attempt at a solution

Not sure how to start this one. Any suggestions?

Last edited by a moderator: Apr 24, 2017
2. Oct 26, 2009

### willem2

I have no idea what all those lengths are. You probably need the fact that the torque around
the point where the tray is supported is 0 if it is in equilibrium.