Review Newton's Laws

Document Sample
Review Newton's Laws Powered By Docstoc
					           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