Friday, May 13, 2011

Announcements:

• If your clicker seems to not work properly or the Low Battery light comes on, let me know, and do not put it back in the storage case.
• Remember to work through example problems in your book before doing homework problems.
• The UNC Learning Center is offering free tutoring this summer Mondays – Thursdays from 1-9 pm in Dey Hall rooms 205 & 207. For more information, call 962-6389 or go to http://learningcenter.unc.edu

Assignments:

• HW2 is now due tonight
• Submit HW3 before midnight Sunday.
• Read Chapter 4 and submit HW4 by midnight Monday.
• RWP3 - Bank Robbery  (hand in during class on Tuesday)

Chapter 2:

Chapter 2 ConceptTests using clickers

Draw graphs of vertical position, velocity, and acceleration as functions of time for a ball thrown up to a height of 5 m and then caught at the initial level.

Chapter 3:  Vectors

Vectors and components: 

Vectors A and B have the same magnitude and orientation.  Does A = B?

Vector A is 10 m long and oriented 30 degrees above the positive x axis.
(T/F):  Does A = A_x + A_y ?

A = A_xx + A_yy
A = Acos30x + Asin30y
A = Asin60x + Acos60y

The top of a tree is 30 degrees above horizontal when viewed from a distance of 50 feet from its base.  What is the approximate height of this tree?
A)  20 ft.    B)  30 ft.    C)  40 ft.    D)  50 ft.    E)  60 ft.

Methods for vector addition:
 - Graphically using tail-to-head or parallelogram method
 - Components or unit-vector notation

Example problem:  An airplane flies with an airspeed of 100 m/s at a compass heading of 120 degrees.  What is the displacement of this plane after 5 minutes, assuming there is no wind?  What if there is wind from the north at 20 m/s?

Note:  Angle measurements for a compass heading are not the same as polar coordinates that correspond to a Cartesian coordinate system!

Chapter 3 ConceptTests using clickers

Minute Paper:

• What is the most important thing you learned today (or this week)?
• What questions or concerns do you have?

Chapter 4:  Motion in Two Dimensions

Same physics as 1D motion.  Simply treat each component independently and add vectors.

Tips for solving kinematics problems:

• Displacement is a vector, distance is a scalar and is always bigger than |displacement|.
• In free-fall, horizontal velocity is constant (gravity only affects vertical component).
• Use final velocity components to find final speed (resultant).
• Speed is a scalar and therefore is always positive.