Physics 2211: Lecture 16

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Physics 2211 Lecture 16

• Nonzero acceleration
• Newtons 2nd Law
• Mass and Weight

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Lightning Review of Newtons Laws
Force is required to have acceleration aF/m
Acceleration produces changes in speed and/or
direction. Therefore,
Force is required to have changes in speed or
direction of motion
Constant velocity motion does not require
acceleration. Therefore,
Force is not required to have motion
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Using Newton's 2nd Law

• Law 2 For any object, FNET maWhere FNET
  ??F
• The objects trajectory can be determined
• using a in the equations of kinematics.

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A 1500 kg car is pulled by a tow truck. The
tension in the tow rope is 2500 N. A 200 N
frictional force opposes the motion. If the car
starts from rest, what is its speed after 5.0sec?
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Mass and Weight

• Mass is an intrinsic property
  of matter measured in kg.
• Weight is the gravitational force
  exerted on an object by a planet.

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Measuring mass and weightthe spring scale
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A block of mass m rests on a spring scale. The
scale sits on the floor of an elevator moving up
at constant speed. How is the magnitude of the
measured spring force F related to the weight w?

• F gt w
• F w
• (3) F lt w

Correct Answer is 2
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A block of mass m rests on a spring scale. The
scale sits on the floor of an elevator that is
slowing down as is moves upward. How is the
magnitude of the measured spring force F related
to the weight w?

• F gt w
• F w
• (3) F lt w

Correct answer is 3
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Weightlessness

• Elevator cable breaks, and elevator
  free-falls.

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Recap
Newtons 2nd Law Non-zero
acceleration problems Mass and Weight
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