Can someone please answer this for me, thanks:

Can an object be moving and still be in equilibrium? Explain.

Yes. If an object is not moving relative to you and I am moving relative to you, then relative to me, the object will be moving. The laws of physics are the same for all non-accelerating observers.

When defining what we mean by "equilibrium", you will want that definition to be independent of the observer. You don't want to define "equilibrium" such that according to you an object can be in equilibrium but according to me it isn't just because I'm moving relative to the object.

what is mean about forces acting on a book if we state that the book is in a state of equilibrium

Yes, an object can be moving and still be in equilibrium. To understand this concept, it's important to grasp the concept of equilibrium and the different types of equilibrium.

Equilibrium refers to a state where an object is balanced and experiences no net force or torque. There are two types of equilibrium: static equilibrium and dynamic equilibrium.

1. static equilibrium: In static equilibrium, an object is at rest and doesn't move. It occurs when the sum of all the external forces acting on the object is zero, and the sum of all the torques (rotational forces) acting on the object is also zero. This means that the object is perfectly balanced, with no forces or torques causing it to move.

2. dynamic equilibrium: In dynamic equilibrium, an object is moving but still experiences no net force or torque. This occurs when the object's velocity remains constant in both magnitude (speed) and direction. To be in dynamic equilibrium, the object must have balanced forces acting on it.

Imagine a car moving at a constant speed on a straight, level road. If the car maintains a constant velocity without any acceleration or deceleration, it is in dynamic equilibrium. Even though the car is moving, the net force acting on it is zero because the forces pushing the car forward (like the engine force) are balanced by the forces opposing its motion (like friction). Similarly, the torques acting on the car are also balanced, keeping it in equilibrium.

In summary, an object can be moving and still be in equilibrium if the sum of all the forces and torques acting on it is zero, resulting in a balanced state.