An object has a mass of $10\,\text{kg}$. For each case below answer the questions and provide an example.
1. If an object is moving, is it possible for the net force acting on it to be zero?2. If the acceleration of an object is zero, are no forces acting on it?3. Only one force acts on an object. Can the object have zero acceleration?4. Only one force acts on an object. Can it have zero velocity?

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Jason · Accepted Answer

1. Yes. An object moving with constant velocity has zero acceleration, so the net force is $0\,\text{N}$ (for example, a $10\,\text{kg}$ mass sliding at constant speed on a frictionless surface).2. No. Zero acceleration means the net force is $0\,\text{N}$, but multiple forces can act on the object and balance each other (for example, a $10\,\text{kg}$ object at rest on a horizontal surface where the downward gravitational force balances the upward normal force).3. No. If only one force acts on an object, the net force cannot be $0\,\text{N}$, so by Newton&#8217;s second law ($\Sigma \vec{F} = m\vec{a}$), the acceleration cannot be $0\,\text{m/s}^2$ (for example, a $10\,\text{kg}$ object in free fall under gravity alone).4. Yes. An object subjected to a single force can momentarily have a velocity of $0\,\text{m/s}$ (for example, a $10\,\text{kg}$ object thrown vertically upward has a velocity of $0\,\text{m/s}$ at the peak of its trajectory while gravity acts on it).

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