Answer:
An object in equilibrium has a net force of zero
Static equilibrium describes an object at rest having equal and balanced forces acting upon it.
Dynamic equilibrium describes an object in motion having equal and balanced forces acting upon it.
Explanation:
An object is said to be in equilibrium when a net force of zero is acting on it. When this condition occurs, the object will have zero acceleration, according to Newton's second law:

where F is the net force, m the mass of the object, a the acceleration. Since F=0, then a=0. As a result, we have two possible situations:
- If the object was at rest, then it will keep its state of rest. In this case, we talk about static equilibrium.
- If the object was moving, it will keep moving with constant velocity. In this case, we talk about dynamic equilibrium.
C is the best answer
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Answer:
Orbital Time Period is 24 years
Explanation:
This can be explained by the definition of time period.
Time period can be defined as the time taken by an object to complete one cycle, here, time taken to complete one revolution.
Also, we know that an extra solar planet which is also called as an exo planet is that planet which is outside our solar system and orbits any star other than our sun. The system in consideration is extra solar system with a single planet.
Therefore, the time taken by the parent star to move about its mass center is the orbital time period that is 24 years.
First of all Longitudinal waves is a matter in the medium that moves parallel to the direction of the wave travels.
1st example: sound travels parallel.
2nd example: when you talk you will here your voice again. because all the frequency bounce back to you.
In the other hand Transverse wave matter in the medium moves perpendicular to direction the wave travels.
For example: light is a good example of transverse wave.