Figure (5.Q4) shows a heavy block kept on a frictionless surface and being pulled by two ropes of equal mass m. At t = 0, the force on the left rope is withdrawn but the force on the right end continues to act.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.
a.) At t<0, the body is in equilibrium, thus the forces on left and right must be equal.
for t<0
b.) This option is incorrect because the term 
is a vertical force and thus cannot be fitted into the given equation as the given equation represents horizontal forces .
c.) Since the force on the left is withdrawn then 
and 
since it has not been withdrawn . Thus this option is incorrect.
d.) 
is non-zero but 
, thus, instead of
it should be written as 
. Thus this option is also incorrect.