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Boxes and a Pulley 
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#1
Oct1407, 04:31 PM

P: 67

In the figure below, three ballot boxes are connected by cords, one of which wraps over a pulley having negligible friction on its axle and negligible mass. The masses are mA = 22.0 kg, mB = 40.0 kg, mC = 30.0 kg.
figure: PulleymA    mB  mC Now I apply Fnet = ma so. . . the massA in the x direction would be T1 (tension) = (mA)(ax) and in the Y direction n(mA)(g) = (mA)(ay). the massB in the y direction would be T1T2  (mB)(g) = (mB)(ay) the massC in the y direction would be T2  (mC)(g) = (mC)(ay) but in the equations above wouldnt acceleration in the x direction (ax) = 0? and accel. in the y (ay)direction be (9.8 m/s^2 aka gravity (g)) 


#2
Oct1407, 07:57 PM

HW Helper
P: 4,125

No ax isn't 0. The acceleration of mA towards the left equals the acceleration of the hanging masses downwards...
using your conventions ax = ay. so you have 3 equations with 3 unknowns... T1, T2 and ax. One "trick" you can use to simplify calculating T1 and ax, is to take mB and mC together as one system. that way you get 2 equations with 2 unknowns, T1 and ax. But the 3 equations you have seem fine. 


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