Answer:
B) momentum and mechanical energy
Explanation:
In classical physics, a closed system is a system that does not exchange any matter with the surrounding, and on which there are no external forces acting on it.
Due to this definition, we have the following consequences:
- In a collision in a closed system, momentum is always conserved. This is because there is exchange of matter with the surroundings (so, no mass can be lost), and also because there are no external forces acting on the objects inside the system. In fact, the variation of the total momentum of the system is related to the net force acting on the system:
but since the net force F is zero, then the variation of momentum, 
, is also zero, therefore the momentum is constant.
- Also, mechanical energy is conserved. Mechanical energy is the sum of potential energy and kinetic energy of the system: again, since there are no external forces acting on the system, energy cannot be dissipated, so the total energy of the system cannot change.
<u>Yes, work is done when a book falls of the table.</u>
This is because:
When the book falls, it's potential energy is converted into kinetic energy. As it reaches the floor down, this kinetic energy is converted to heat energy and sound energy due to the impact.
When a force is imposed on an object to cause displacement of that object, work is done on that object. For a force to do work on an object, there should be a displacement and this force should cause the displacement. So here, since the book falls from the table and causes the displacement of the book from the table to the floor. It is said that work is done.
Work can be given by the formula:
W = F • d
where F is the force and d is the displacement.
1. Answer: 7.75 seconds
Explanation: 76-14=62 metres
62/8=7.75 seconds
2. Answer: 2.5 seconds
Explanation: 28-18=10 metres
10/4=2.5 seconds
Answer:
A causes free electrons to flow
Explanation:
The amount of force that causes electrons to flow in a conductor is called electromotive force.
