In the arrangement shown in the figure, The ends P and Q of an unstretchable string move downwards with uniform speed “v”. Pulleys A and B are fixed. Mass M moves upwards with a speed?

The block of mass m is moving up with a speed of 2*v*cos(phi)

Let the speed of mass M be v .The point on thread just connected to mass M will also have the same velocity .The component of the v along the thread is v cos θ . That means any point on the thread must be moving with speed v cos θ .As it is given that thread is moving with velocity u .That meansv cos θ = u