A painter is hanging in a cage on the outside of a building. When the painter, who weighs 1000N pulls on the rope he exerts a force on the floor of the cage of 450N. The cage weighs 250N. Find the acceleration.

The tension in the rope balances the man and cage and the system is in equilibrium. The cage only moves when the force of 450 N is applied.

So, I reckon

450 = ma

the force has to overcome the weight of man and cage so

F = 1000 + 250 = mg

so, m = 1250/10 = 125 kg

therefore

450 = 125a

$a = 3.6 m/s^2$

My book has $2 m/s^2$ can anyone explain this?