일반물리학 1 — Force and Motion-I: Problem 50

50 In Fig. 5-36, three ballot boxes are connected by cords, one of which wraps over a pulley having negligible friction on its axle and negligible mass. The three masses are $m_A = 30.0 \text{ kg}$, $m_B = 30.0 \text{ kg}$, and $m_C = 10.0 \text{ kg}$. When the assembly is released from rest, (a) what is the tension in the cord connecting B and C and (b) how far does A move in the first $0.250 \text{ s}$ (assuming it does not reach the pulley)?