# phyics help nedded

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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 = 24.0 kg, mB = 40.0 kg, mC = 30.0 kg.

(a) When the assembly is released from rest, what is the tension in the cord that connects boxes B and C?
N

(b) How far does box A move in the first 0.250 s (assuming it does not reach the pulley)?
m

• phyics help nedded -

(a) m(A)a=T1
m(B)a=m(B)g-T1+T2
m(C)a=m(C)g-T2
a{m(A) + m(B)+m(C)} = T1+ m(B)g-T1+T2 + m(C)g-T2 =g{ m(B)+m(C)}
a= g{ m(B)+m(C)}/{ m(A) + m(B)+m(C)} =9.8(40+30)/(24+40+30) =7.3 m/s²

T1 =m(A)a=24•7.3=175.2 N
T2 = m(C)(g-a) = 30•(9.8-7.3)= 75 N

(b) s=at²/2 = 7.3•0.25²/2 = 0.228 m

• phyics help nedded -

So how can we state the appropriate answer to part (a)...?

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