Laws of MotionHard

Question

A heavy block kept on a frictionless surface and being pulled by two ropes of equal mass m as shown in figure. At t = 0, the force on the left rope is withdrawn but the force on the right end continues to act. Let F1 and F2 be the magnitudes of the forces by the right rope and the left rope on the block respectively.

Options

A.F1 = F2 = F        for  t < 0
B.F1 = F2 = F + mg   for  t < 0
C.F1 = F,    F2 = F  for  t > 0
D.F1 < F,    F2 = F     for  t > 0

Solution

(A) For t < 0 As net force on system is zero, therefore acceleration of the system is zero
∴    F1 = F2 = F    for t < 0 

For t > 0 system is accelerated given by

F - F1 = ma
F1 = F - ma     ............... (1)

F1 - F2 = Ma
F1 = F2 +  Ma     .............. (2)

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