Review: Newton's Laws

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Review Newton's Laws

• Law 1 An object subject to no external forces
  is at rest or moves with a constant velocity if
  viewed from an inertial reference frame.
• Law 2 For any object, FNET maWhere FNET
  ??F
• Law 3 later

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Physics 2211 Lecture 09/17/04 FriTodays Agenda

• 1-D motion Dynamics
• Equilibrium problem solving strategies
• Static and Dynamic Equilibrium Problem

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In 1D, objects move in a straight line (cars,
bycicles, runners, etc) We develop strategy for
solving force and Motion problems. Forces
WEIGHT, TENSION, THRUST, FRICTION, AND DRAG.
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EQUILIBRIUM

• If the net force on an object is zero, the
  object is in equilibrium
• STATIC EQUILIBRIUM object is at rest
• DYNAMIC EQUILIBRIUM object is moving along a
  straight line

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EQUILIBRIUM PROBLEMS
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Problem 1
The three ropes in the figure are tied to a
small, very light ring. Two of the ropes are
anchored to walls at right angles, and the third
rope pulls as shown. What are T1 and T2, the
magnitudes of the tension forces in the first
two ropes?
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(No Transcript)
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Question 1
A 20kg loudspeaker is suspended 2.0m below the
ceiling by two 3m long cables that angle outward
at equal angles. What is the tension in the
cables?
1) 20 N 2) 102 N 3) 147 N 4) 211
N 5) 367 N
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(3) 147N
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Problem 2

• A car with a weight of 15000 N is being towed up
  a 20deg slope at constant velocity. The tow rope
  is rated at 6000 N maximum tension. Will it break?

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Rope will not break
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QUESTION 2
In an electricity experiment, a 1.0g plastic ball
is suspended on a 60-cm long string and given an
electric charge. A charged rod brought near the
ball exerts a horizontal electrical force
on it, causing the ball to Swing out to a 20deg
angle and remain there. a) What is the
magnitude of ?

• 0.003N
• 0.011N
• 0.02N
• 0.0024N
• 5) 0.0036N

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5) 0.0036N
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QUESTION 2
In an electricity experiment, a 1.0g plastic ball
is suspended on a 60-cm long string and given an
electric charge. A charged rod brought near the
ball exerts a horizontal electrical force
on it, causing the ball to Swing out to a 20deg
angle and remain there. a) What is the tension
in the string?

• 0.045N
• 0.0104N
• 0.0220N
• 0.0308N
• 5) 0.0405N

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2) 0.0104N