答：jrtc27
看了你的问题，我觉得可以用如下代码实现这个效果：

b2Vec2 impulseB = bodyB->GetPosition() - bodyA->GetPosition();
impulseB /= impulseB.Length();
impulseB *= predefinedScaleValue; // predefinedScaleValue is your velocity
b2Vec2 impulseC = -impulseB;
bodyB->ApplyLinearImpulse(impulseB, bodyB->GetWorldCenter());
bodyC->ApplyLinearImpulse(impulseC, bodyC->GetWorldCenter());