Box2d: mousejoint jerky

Question

Hi to all!

I'm making my first iPhone game.

I have increasing number balls that can be dragged. I had some problems with inertial delay of mousejoint and I configured them as follows:

b2MouseJointDef md;
md.body1 = _groundBody;
md.body2 = body;
md.target = p;
md.maxForce = 10000.0f * body->GetMass();
md.dampingRatio = 0;
md.frequencyHz = 100;
_world->CreateJoint(&md);

When I have 10/15 balls all is ok.

When I have 30/40 balls the overall performance seems to be ok but the dragging operation behaves jerky.

Is it a problem related to frequencyHz? Am I doing something wrong?

Thanks!