9/7/11. Which of the following is not a vector? Physics 101 Tuesday 9/6/11 Class 4

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1 Reading Quiz Which of the following is not a vector? Physics 101 Tuesday 9/6/11 Class 4 Chapter 3 Sections Free fall Components of a Vector Adding and Subtracting Vectors Unit Vectors A: speed B: velocity C: displacement D: position E: I think more than one of these is not a vector Freefall If you drop an object in the absence of air resistance, it accelerates downward at 9.8 m/s^2. If instead you throw it downward, its downward acceleration after release is A: less than 9.8 m/s^2. B: 9.8 m/s^2. C: more than 9.8 m/s^2. Eric Mazur, "Peer Instruction" 1997 Free fall question 1 You throw a ball straight up into the air. After it leaves your hand, at what point in it s flight does it have the maximum value of acceleration? A) its acceleration is constant everywhere B) at the top of the trajectory C) halfway to the top of the trajectory D) just after it leaves your hand E) just before it returns to your hand 1

2 Freefall You throw a ball straight up into the air with an initial speed of 10 m/s. Assuming no air resistance, what is its speed when it returns to you? A) More than 10 m/s B) 10 m/s C) less than 10 m/s D) need more information Freefall equations A person standing at the edge of a cliff throws one ball straight up and another ball straight down at the same initial speed. Neglecting air resistance, the ball to hit the ground below the cliff with the greater speed is the one initially thrown A: upward. B: downward. C: neither they both hit at the same speed Eric Mazur, "Peer Instruction" 1997 Free fall Constant acceleration equations A ball is launched straight up with initial velocity v o. (Neglect air resistance) If the initial velocity v o is doubled, the time to reach the apex of the trajectory... A: doubles. B: increases by a factor of 4. C: Neither of these. D: Not enough information given. 2

3 Constant acceleration equations A ball is launched straight up with initial velocity v o. (Neglect air resistance) If the initial velocity v o is doubled, the maximum height of the ball... A: doubles. B: increases by a factor of 4. C: Neither of these. D: Not enough information given. Constant acceleration equations On Planet X, a rock is thrown straight up. The position and velocity of the ball at various times are listed below. (Note: I chose "up" as the "+" direction) Time(s) Height(m) What is the acceleration due to gravity on Planet X? A: -5 m/s^2...b: -10 m/s^2 C: -15 m/s^2...d: -20 m/s^2 E: None of these Constant acceleration equations On Planet X, a rock is thrown straight up. The position and velocity of the ball at various times are listed below. (Note: I chose "up" as the "+" direction) Time(s) Velocity (m/s) Vectors Concept Question 1 What is the acceleration due to gravity on Planet X? A: -5 m/s^2...b: -10 m/s^2 C: -15 m/s^2...d: -20 m/s^2 E: None of these 3

4 Concept Question 2 Question 2 4

5 If two vectors are given such that A + B = 0, what can you say about the magnitude and direction of vectors A and B? A) Same magnitude, but can be in any direction B) Same magnitude, but must be in the same direction A C) Different magnitudes, but must be in opposite directions D) Same magnitude, but must be in opposite directions E) Different magnitudes, but must be in opposite directions If two vectors are given such that A + B = C, and A 2 + B 2 = C 2, how are vectors A and B oriented with respect to each other? A) They are perpendicular to each other B) They are parallel and in the same direction A C) They are parallel but in opposite directions D) They are at 45 to each other E) They can be at any angle to each other If two vectors are given such that A + B = C, and A + B = C, how are vectors A and B oriented with respect to each other? A) They are perpendicular to each other B) They are parallel and in the same direction C) They are parallel but in opposite directions D) They are at 45 to each other E) They can be at any angle to each other 5

6 If each component of a vector is doubled, what happens to the angle of that vector? A) it doubles B) it increases, but by less than double C) it does not change D) it is reduced by half E) it decreases, but not as much as half You are adding vectors of length 20 and 40 units. What is the only possible resultant magnitude that you can obtain out of the following choices? A) 0 B) 18 C) 37 D) 64 E) 100 A certain vector has x and y components that are equal in magnitude. Which of the following is a possible angle for this vector in a standard x-y coordinate system? A) 30 B) 180 C) 90 D) 60 E) 45 Next Week Reading Assignments: Thursday 9/8 sections Tuesday 9/13 sections

7 Next Week Next few slides were extras, in case we had time. Extra You throw a baseball glove straight up in the air with an initial speed of 9.8 m/s. How long does the glove take to return to your hand? A) 1 sec B) 2 sec C) 3 sec D) 4 sec Extra Extra problems You throw a baseball glove straight up in the air with an initial speed of 9.8 m/s. How long does the glove take to get to it s highest point? A) 0.5 sec B) 1 sec C) 1.5 sec D) 2 sec You shoot an arrow up into the air, 2 seconds later the arrow has gone straight up to a height of 30 m above the launch point. What was the arrows initial speed? A) 12 m/s B) 24 m/s C) 48 m/s D) 60 m/s 7

8 Extra problems You shoot an arrow up into the air, 2 seconds later the arrow has gone straight up to a height of 30 m above the launch point. How long did it take for the arrow to reach 15m? Next Week Reading Assignments: Thursday 9/8 sections Tuesday 9/13 sections A) >1 s B) <1 s C) =1 s 8