# 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 = ma

Where FNET = F

Law 3:      later

Physics 2211, Pg 1
Physics 2211: Lecture 09/17/04
Fri

Today’s Agenda
1-D motion: Dynamics

Equilibrium : problem solving strategies

Static and Dynamic Equilibrium
Problem

Physics 2211, Pg 2
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.

Physics 2211, Pg 3
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

Physics 2211, Pg 4
EQUILIBRIUM PROBLEMS

Physics 2211, Pg 5
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?
Physics 2211, Pg 6
Physics 2211, Pg 7
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

Physics 2211, Pg 8
(3) 147N

Physics 2211, Pg 9
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?

Physics 2211, Pg 10
Fnet x,   F  T  n  w  0
x   x   x    x

Fnet y,   F  T  n  w  0
y   y    y   y

Tx  T , Ty  0
nx  0; n y  n
wx   w sin  ; wy   w cos 
T  w sin  0
n  w cos  0
T  w sin  5130 N

T  6000 N            Rope will not break
Physics 2211, Pg 11
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 F on it, causing the ball
elec
to
Swing out to a 20deg angle and remain there.

a) What is the magnitude of     Felec   ?

1)   0.003N
2)   0.011N
3)   0.02N
4)   0.0024N
5)   0.0036N

Physics 2211, Pg 12
5) 0.0036N

Physics 2211, Pg 13
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 F on it, causing the ball
elec
to
Swing out to a 20deg angle and remain there.

a) What is the tension in the string?

1)   0.045N
2)   0.0104N
3)   0.0220N
4)   0.0308N
5)   0.0405N

Physics 2211, Pg 14
2)   0.0104N

Physics 2211, Pg 15

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