PHY 121 Ch 5 Lecture

# PHY 121 Ch 5 Lecture - Lecture 7 Tuesday February 5 1 A...

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1 Lecture 7 Tuesday, February 5

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2 A body is in equilibrium A. If the object is at rest. B. If the object’s velocity is constant. C. If the object’s acceleration is constant. D. If the object is not subject to gravitational forces.
3 In an equilibrium problem involving two objects, the magnitude of three forces is unknown. A. It is impossible to find the unknown magnitudes. B. It is often possible to find the magnitudes because one can write more than three equations. C. In an equilibrium situation all forces are zero. D. It is possible to find the magnitudes because they add up to zero.

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4 The apparent weight of an object A. is the magnitude of the contact force that supports the object. B. is the magnitude of the force of gravity. C. is the acceleration of gravity in vacuum. D. is weight of the object minus its mass.
5 An object is attached to a vertical string. The mass of the string is negligible compared to the mass of the object A. The tension in the string is equal to the weight of the object. B. The tension in the string is less than the weight of the object. C. The tension in the string is larger than the weight of the string. D. More information is needed to tell which of the two forces has a larger magnitude.

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6 Mass and force • Mass is a property of an object. An object has a mass regardless of whether a force is applied to the object or not. • Usually the force applied on an object is independent of its mass. But the object’s acceleration depends on the force and the mass through Newton’ second law. ! a = ! F ! m This is the object’s response This is what others do to the object This is a characteristic property of the object
7 Mass and force II • Mass is not the only property an object can have.

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PHY 121 Ch 5 Lecture - Lecture 7 Tuesday February 5 1 A...

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