Warm-Up: September 22, 2015 Complete the table VariableSymbolSI Unit of MeasurementSI Symbol Timetsecondss x m/s meters per second squared

Homework Questions?

Scalar vs. Vector  Scalar – A quantity with only magnitude. Temperature Mass Density Speed  Vector – A quantity with both magnitude and direction. Velocity Acceleration

Subscripts and Symbols  f  final  i  initial  0  initial (time = zero)  No subscript  final  Δ = delta = change = final – initial  Bar above variable = average It is often omitted

Equations

Adding Vectors in 1D  The resultant is the sum of two or more vectors.  If they are in the same direction, add their magnitudes.  If they are in opposite directions, subtract their magnitudes. The direction of the resultant is in the direction of the larger vector.

Adding 2-D Vectors  Place vectors tip to tail  Draw an arrow from the tail of one to the tip of the other (complete the triangle) This is the resultant  Use Pythagorean Theorem to find the magnitude if the vectors are perpendicular

You-Try #1  Find the resultant of the following pairs of vectors: a) 3 m right and 7 m left b) 2 m up and 5 m up c) 4.0 m North and 3.0 m East d) 2.0 m North and 3.0 m West

Motion Graphs Distance vs. Time Velocity vs. Time Horizontal axis Time Vertical axisDistanceVelocity DistanceLineArea under the line VelocitySlope of lineLine AccelerationSlope of line

Example 2  Use the following velocity vs. time graph to determine how far the object traveled after 5.0 seconds. After 10.0 seconds.

You-Try #2  Use the following velocity vs. time graph to determine how far the object traveled after 15.0 seconds. After 20.0 seconds.

Breakdown Method 1. What information does the problem give me? 2. What is the question asking for? 3. What formula(s) do I need? 4. Check for unit consistency 5. Replace variables in the formula with the numbers in the problem. 6. Calculate the correct answer. 7. Is the answer reasonable?

Warm-Up: September 23/24, 2015  A penny is dropped from a 137 meter tall building onto the street below. Gravity accelerates it at a constant 9.8 m/s 2 (ignoring air resistance). How far has the penny fallen after 2.0 seconds? After 10. seconds?

Assignment  Review Worksheet – available on the web site. Answer questions on lined/graph paper. Due Friday  You have the rest of class to work with your partner on it.

Kinematics Review Worksheet  Should be completed in class today  You may work with 1 or 2 other people (no groups larger than 3)

Warm-Up: September 25, 2015  A cannon ball is launched upward at 105 m/s from the edge of a ship 4.7 m above the surface of the ocean. Gravity accelerates it downward at 9.8 m/s 2. How high above the ocean is the cannon ball 3.0 seconds after launch?

Kinematics Review Answers  1) Breakdown Format – from notes  2) Vector includes direction, scalar does not  3) Final – initial  4) 78 m  5) 12 s  6) Velocity includes direction, speed does not  7) 1.0x10 2 m

Kinematics Review Answers  8) A – Accelerating  8) B – Moving forward (in positive direction) at a constant speed  8) C – Moving backward (in negative direction) at a constant speed  8) D – At rest  9) -1.8 m/s

Kinematics Review Answers  10A) 14 m/s west  10B) 4 m/s east  10C) 4.2 m/s right  10D) 4.6 m/s NE  10E) 3.4 m/s SW

Kinematics Review Answers

Kinematics Questions?

Assignment Solutions  Solutions to the chapter 3 assignment are posted online.  Solutions to the chapter 2 assignment will be posted online by the end of the day.  Check your work over the weekend.

You-Try: Page 82 #93  A plane changes its velocity from 145 m/s to 75 m/s in 15 s. a) What is the plane’s average acceleration? b) Assuming the plane’s acceleration is constant, how far does the plane fly in the 15 s?

You-Try: Page 84 #115  A helicopter is rising at 5.0 m/s when a bag of its cargo is dropped. The bag falls for 2.0 s. a) What is the bag’s velocity? b) How far has the bag fallen? c) How far below the helicopter is the bag?

Netbooks – Review Game  Partner up with 1 other student  Only 1 netbook per pair   “Kinematics Review Game”  Have desks cleared enough to safely rest your netbook on the desk

Warm-Up:  A car accelerates from 10 m/s to 35 m/s in 5.7 seconds. What is the car’s average acceleration?

Acceleration Lab  Read the opening paragraph and write a hypothesis.  Read through the lab paper.  You will be assigned your lab group.