Mechanic about wood block, friction and pulley

[stranger123]

Homework Statement

Two objects A and B weighing 50 N and 80 N respectively were connected by a light string over a fixed pulley. A was put on a reasonably long and horizontal table surface. The coefficient of sliding friction between A and the table surface is μ = 0.3 while the friction between the string and the pulley is neglected. Find the velocity of B after falling downwards for 2m. (Take g = 10 ms^-2)
Wa = 50 N
Wb = 80 N
μ = 0.3

The Attempt at a Solution

The question given that the object B falls when at start, thus when object B falls the tension change as the angle change, can't even start the 1st equation.

 

[stranger123]

any1 can help?? i still can't figure how to do this, this question is past year exam question but there's only answer provided. the ans is 2√2