Physics - Force problem....?

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struttinhoyt

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A box weighing 77.0 N rests on a table. A rope tied to the box runs vertically upward over a pulley and a weight is hung from the other end. Determine the force that the table exerts on the box is the weight hanging on the other side of the pulley weighs A. 30.0 N B. 60.0 N and C. 90.0 N....
 
Force normal = FgravityOnFirstBox - FgravityHangingBox

So, for 30 N box on other side:
Fnormal = 77 - 30 = 47.0 N

for 60 N box...
Fnormal = 77 - 60 = 17.0 N

for 90 N box...
Fnormal = 77 - 90 = -13 N, so the box is lifted off the ground up to the pulley because the second box weighs more.
 
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