RevoluteJointDef rjd = new RevoluteJointDef();
rjd.initialize(prevBody, body, new Vec2(0.0f, 17.0f));
getWorld().createJoint(rjd);
PrismaticJointDef pjd = new PrismaticJointDef();
pjd.initialize(ground, body, new Vec2(0.0f, 17.0f), new Vec2(0.0f, 1.0f));
pjd.maxMotorForce = 1000.0f;
pjd.enableMotor = false;
m_joint2 = (PrismaticJoint) getWorld().createJoint(pjd);