17. As difficult as it is to visualize the changes in velocity, a good understanding of acceleration is needed to master kinematics problems. Recognizing that acceleration can be positive, while velocity is negative (and vice versa) can be challenging. a. Object is speeding up (from still) in the positive direction. For example, a ball is placed on a slanted ramp. Velocity is positive / zero / negative and increasing / constant /decreasing. Acceleration is positive / zero / negative. b. Object is speeding up (from still) in the negative direction. For example, a ball is placed on a ramp that is slanted towards the negative direction (eg. down to the left). Velocity is positive / zero / negative and increasing / constant /decreasing. Acceleration is positive / zero / negative. c. Object is slowing down in the positive direction. For example, you push a ball up a slanted ramp. Velocity is positive / zero / negative and increasing / constant /decreasing. Acceleration is positive / zero / negative. d. Object is slowing down in the negative direction. For example, you push a ball up a ramp that is slanted towards the negative direction (eg. down to the right). Velocity is positive / zero / negative and increasing / constant /decreasing. Acceleration is positive / zero / negative. 18. Review your results from the previous question to build general statements that are always true: Acceleration is always in the opposite direction of if the object is slowing down. Acceleration is always in the same direction of if the object is speeding up.1. The pool ball shown below was photographed 8 times at equal time intervals. Is the pool ball's motion uniform? How do you know? Sketch a d vs t and v vs t graph, showing the general shape of each graph. 2. Make a sketch of what the pool ball's photos would look like if it were accelerating (both positively and negatively). 3. Acceleration is often a difficult term to understand. How could you best explain the acceleration of a car (and how it's different then velocity) to a non-physicist? 4. How can you recognize uniform motion on a d vs t graph? 5. What are common units for the following: a. Displacement / Distance (provide 6 examples and circle the SI standard one): b. Time (provide 3 and circle the SI standard one): c. Velocity / Speed (provide 4 and circle the SI standard one): d. Acceleration (provide 3 and circle the SI standard one):10. 11. 12. 13. A toboggan accelerates from rest at 1.1 misE. After 10. seconds, how fast is it going? Show the equation used and all steps. At the bottom of the hill, the toboggan moving 12 mfs forward accelerates at -0.50 mls2 for 10 5. What is the toboggan's velocity at the end of the 10 5? Show the equation used and all steps. How much time does it take a car travelling south at 12 ms to increase its velocity to 26mls south if it accelerates at 3.5 mls2 south? Show the equation used and all steps. The acceleration of a freely falling object (near Earth), when we assume no air resistance, is {remember units). The assumption of no air resistance is never totally true but is often close enough to make pretty accurate calculations. Discuss the properties of free-falling masses where this is a really good assumption and when it isn't. An apple falls from a tree heading directly for Newton's head. What is its velocity after 1 second? After 2 seconds? A ball is thrown straight up into the air at 14 mils. How long does it take for the ball to slow down to an upward velocity of6.0 mis? Show the equation used and all steps. If you throw a rock up into the air, when is its velocity zero? What is the acceleration when the velocity is zero? 14. A rock is thrown downwards with an initial velocity of 8.0 mfs. What is the velocity of the rock after 1.5 s? 15. The direction of acceleration is determined by the change in velocity (Av = Vf v0). Complete the following table, then below the table invent a situation where these velocities might happen. \"A\" is done for you. a [pas or neg) A. A person. at a stopL'Lgl/itpmsses the gas aw! goes from still (0W5) to loud/S 16. Explain why the following misconceptions are false. a) If acceleration is zero, the object must be standing still. b) Velocity and acceleration are always the same sign (both positive or both negative). c) If speed is increasing, acceleration must be positive. 1. What is a tangent line and what is it used for? Sketch an example. 2. What value is the slope of a v vs t graph for a free-falling object? Why? 3. If wind resistance was included in the previous question, would the slope get bigger or smaller? 4. Describe the Apollo 15 experiment involving the hammer and feather. Explain why this doesn't work on Earth. 5. What is the acceleration shown in the following graph? Velocity vs. Time 40 30 Velocity (m/s [forward]) 10 Time (s) 6. Sketch d vs t and v vs t graphs for a stone that was dropped off a 30 m cliff. Just the rough shape and highlights is good. 7. Sketch d vs t and v vs t graphs for a stone that was thrown upwards at 5 m/s. Just the rough shape and highlights is good