Extra Office Hours/Help

• EXAM I is on Wednesday in class!!!• Chapter 1 – 6. One 8.5”x11” sheet of paper (one

side) allowed for notes.• Tomorrow’s discussion sections with Aditi will be

help sessions for the exam: come with questions!

• Office hours:– DVB Monday 3:00 to 4:00.– Aditi Raval Monday forum: 1:30 to 2:30

SW 331: 2:30 to 3:30

– DVB Tuesday 3:00 to 5:00.

DVB- Review/Summary(* -> topics that I think we have emphasized the most)

• UNITS, (dimensional analysis and checking your answers)

• Newton’s Laws: F=ma ; Free body diagrams*• Interpreting graphs• Kinematics*: Big 3, def’s of a(t),v(t) etc., free fall• Vectors: components*, adding*, products (. & x) • 2-D motion*: Projectiles, relative motion,

centripetal acceleration• Friction and Drag• To date we’ve had 9 lectures covering new

material, look carefully at each an glean the 2-3 key points, write review questions, …

DVB- Exam details• NEXT WEDNESDAY (11 Feb.)• 4 multiple choice questions followed by 2 multi-

part (4 or 5) problems for a total of 13 individual questions. Partial credit is available for all.

• If part b uses answer from part a and a is wrong you can still get full credit for b!!

• Some of the 13 are very straight-forward, a few are more challenging.

• Show your work and use a PEN not a pencil!!• Questions at back of chapter and CALM are

pretty good practice in addition to the problems from the chapters.

DVB’s Formula sheet• Newton II and III• K1, K2, K3; g = 9.80 m/s2

• Vector components (if you don’t know trig well), dot and cross products (2 each).

• Centripetal acceleration• Friction: Static, kinetic, drag• Definitions of instantaneous and average

velocity and acceleration.• VAB = VAC + VCB NOTE: VCB = - VBC

• Any notes I’d need on drawing FBD’s

CALM suggestions• Free Body Diagrams (8)• Drag/friction (8)• Vectors (7)• Relative Motion (5)• Uniform Circular motion (4)• Kinematics (3)• Projectile Motion (3)• 17 no-answer

• A soccer player kicks a ball with an initial velocity Vo at an angle of 18.0o above the horizontal and 18.0 m from the goal line. The ball passes the goal line exactly 0.920 seconds after leaving the player’s foot. Neglect drag throughout the ball’s

– What is the acceleration (magnitude and direction) that the ball experiences as it crosses the goal line (but before it hits the net at the back of the goal) ?

– What is Vo (the magnitude of the initial velocity at which the ball was kicked)?

– How far above the ground is the ball when it crosses the goal line?

– …

Sample Exam question

6-

Chapter 6 Examples Assume throughout that the rotation is at a constant rate. Q0: What is the direction of the net force on the ball?

4-

Let’s take the x axis to point East and the y axis to point North, and consider the diagram shown above. Then we have:

|Vpa| = 500kph ; Vpa = [500 sin(20) i + 500 cos(20) j ] kph.

The problem tells us that the ground velocity is Vpg = (800km/2hr) j = 400 kph j

But we know that the velocity of the plane with respect to (wrt) the ground must be the VECTOR sum of its velocity with respect to the air (VPa) and the velocity of the air wrt the ground (i.e. the wind speed and direction which is what the question is asking us to find). Write the vector sum:

400 kph j = [500 sin(20) i + 500 cos(20) j ] kph + Vag

So we have that the wind must have components: Vx= -500 sin(20) = -171 kph and Vy = 400 - 500cos(20) = - 69.8 kph.

Therefore the wind speed is 185kph and it is in the direction 22.2o S of W

VpaVpg

Vag

More Chapter 4 and 5 Examples5-

Chapter 6 Examples