Question

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which statements about equilibrium are accurate?
a skydiver descending at constant velocity under her parachute is in a state of equilibrium.
for a system to be in a sta of equilibrium, there must be no forces exerted on it by the external world.
newtons first law identifies a net force as something that disturbs a state of equilibrium.
for a system to be in a state of equilibrium, it must have zero velocity and zero acceleration.
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Explanation:

• A skydiver descending at constant velocity under her parachute is in a state of equilibrium: When an object is moving at a constant velocity, its acceleration \(a = 0\). According to Newton's second law \(F_{net}=ma\), if \(a = 0\), then \(F_{net}=0\), which means the forces acting on the skydiver (gravity pulling down and air - resistance/parachute force pulling up) are balanced, so she is in equilibrium.
• For a system to be in a state of equilibrium, there must be no net force acting on it: By the definition of equilibrium in physics (translational equilibrium), \(\sum F = 0\). If there is a net force \(\sum F

eq0\), the system will accelerate (\(F = ma\), \(a=\frac{F}{m}
eq0\) if \(m
eq0\)) and not be in equilibrium.

• Newton's first law identifies a net force as something that disturbs a state of equilibrium: Newton's first law states that an object at rest will remain at rest and an object in motion will remain in motion with a constant velocity unless acted upon by a net external force. So, a net force (\(F_{net}

eq0\)) disturbs the equilibrium state (where \(v = constant\) or \(v = 0\)).

• For a system to be in a state of equilibrium, it must have zero velocity and zero acceleration: This is incorrect. A system can be in equilibrium while having a non - zero constant velocity. For example, the skydiver moving at a constant velocity (non - zero) is in equilibrium. The key is that the acceleration \(a = 0\) (from \(F_{net}=ma\), when \(F_{net}=0\)), but the velocity \(v\) can be non - zero.

Answer:

A skydiver descending at constant velocity under her parachute is in a state of equilibrium.
For a system to be in a state of equilibrium, there must be no net force acting on it.
Newton's first law identifies a net force as something that disturbs a state of equilibrium.