N cafeteria tray is being bussed by a waitress. The tray is 0.5 m long and the w

Question

N cafeteria tray is being bussed by a waitress. The tray is 0.5 m long and the waitress is holding the tray at one end. using only one hand. A cup of coffee that weighs 10 N sits on the tray, centered 0.4 m from the end of the tray that the waitress is holding. In order to keep the tray horizontal, the waitress has to push up on the tray using her fingers which are extended 0.1 m from the end of the tray and push down on the tray using her thumb right at the end. Assume, the center of gravity of the tray is at its center. If the waitress wishes to keep the tray balanced and in static equilibrium then, What force does the waitress need to exert using her fingers What force does the waitress need to exert using her thumb

Explanation / Answer

for rotational equilibrium torque about thumb = 0 (for calculating forse from fingure)

10 * 0.4 = Ff * 0.1

Ff = 40N

b)

for static equilibrium vertical forse should br balance

Ft - Ff + 10 = 0

Ft = Ff - 10 = 40 - 10 = 30N

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