1. 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.

2. 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, …

3. 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.

4. 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

5. 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

6. Sample Exam question
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 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? …

7. 6-

8. 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?

9. 4-
Vag
Vpg
Vpa
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 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 cos(20) j ] kph + Vag
So we have that the wind must have components: Vx= -500 sin(20) = -171 kph and Vy = cos(20) = kph.
Therefore the wind speed is 185kph and it is in the direction 22.2o S of W

10. More Chapter 4 and 5 Examples5-

11. Chapter 6 Examples

12. Chapter 7 examples

13. CALM:
Estimate the amount of work performed on a 1200 kg car as it accelerates from rest to 1.2m/s2 over a distance of 150 m. (poorly phrased question)
(25 correct, 4 incorrect; 26 no ans.)
The square root of 2a(150) equals 19 as the velocity. 0.5 times 1200 kg times 19 equals, Newtons (Correct number, incorrect units, and confusing description)
W=F*d F=m*a F=1200kg*1.2m/s2=1440N d=150m W=1440*150=216000J (correct, if one assumes that the force is constant)

14. A weight-lifter performs the following three steps in his lift: 1)
A weight-lifter performs the following three steps in his lift: 1). He raises the barbell to his chest 2). He holds it at his chest for 10 sec. 3). He lowers the barbell back to the ground. Rank algebraically the work performed by gravity in each of the three steps (label them W1, W2 etc.). Repeat the question for the work performed by the weight-lifter. (15 correct; 7 incorrect; 5 uncertain; 28 no answer)
1) W1 moves the bar only in a y-direction, his force of pulling bar up is greater than the force of gravity pulling the weight down. 2)W2 the lifter feels the force of gravity pulling the bar back down. thus to keep the bar from going down he must provide a normal force to keep it from moving for 10 seconds. 3) W3 the lifter only puts the bar back down to the ground, so only force working is directly down thanks to gravity (the answer is ???)
W1=mgh W2=-1/2g(100) W3=-mgh (1 and 3 are true for the lifter, but these appeared to be for gravity, and W2 is wrong).

15. Chapter 7 examples
B). What is the mass of the block? C). How fast is it moving after it has
traveled down the 0.50m under the influence of the force Fr, assuming that
it started from rest?