Common sense should enable you to eliminate some of these. How can it be sliding if it is at rest?
To be "at equilibrium" means that the net force acting is zero, in which case there is zero acceleration.
Now see if you can figure it out.
A hockey puck slides across the ice at a con-
stant speed.
Which of the following is true?
1. The puck is moving and thus not in equi-
librium.
2. The puck can be considered neither at
rest nor in equilibrium.
3. It is in equilibrium.
4. None of these
5. The puck is at rest.
4 answers
Yes, it is in mechanical equilibrium. There is no longer a force acting upon the puck, which is why it remains at a constant speed. There was a force when the stick pushed it, and realistically there would be a very small force of friction which would slightly slow it down, but according to this question, the puck is not slowing down which means there is no friction. Mechanical equilibrium doesn't mean the object has to be at rest, it means that there is no acceleration or change in speed. Like Newton's law says; an object in motion will remain in motion if there are no forces acting upon it.
jsil
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