Dynamics Review

Question

Can an object be moving at 100 km/hr and be in equilibrium? Explain.

Answer 1

As long as it is moving at a constant speed in a straight line, the net force acting on it is zero, the object is not accelerating, and the forces, if any, acting on it are in equilibrium.  Strictly speaking, it is not really correct to say the object is in equilibrium.  We should say the forces acting on it are in equilibrium, which means their vector sum is zero, resulting in no acceleration, per Newton's second law.