PHYSICS 12 Kinematics Review: WCLN.ca 1. The acceleration of a freely falling object (near Earth), when we assume no air resistance, is (remember units). This acceleration (due to gravity) is also called the and is represented by the letter_ 2. The assumption of no air resistance is never totally true, but is often close enough to make pretty accurate calculations. Discuss cases where this is a really good assumption and when it isn't. 3. 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 positive (and visa) is definitely brain exercise. 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. BOL 2019 Page 11 of 17 PHYSICS 12 WCLN.ca 4. Review your results from the previous question to build general statements that are always true: Acceleration is always in the opposite direction of down. if the object is slowing Acceleration is always in the same direction of if the object is speeding up. 5. Show what happens to each of the following kinematic equations when the acceleration is zero (a=0). Once you have simplified, interpret, in words, what the equation is telling us. One equation is done for you. Keep in mind that the kinematic equations are always valid for motion with constant acceleration. However, they are not always useful... a = = (v vo)/t = If a 0 we get 0 = (vf-vo)/t For this equation to be true this means that 0 = (vf-vo) Or vf=vo (velocity is constant if acceleration is zero) i. d = vot + at ii. v = v + 2ad 6. A stationary boat accelerates to 90 km/hr over 1 km. What is the time it takes to do this? BOL 2019 Page 12 of 17 PHYSICS 12 WCLN.ca 7. A braking train can decelerate at 0.4 m/s. If the train is travelling at 160 km/hr and needs to plan to stop at a pick-up area. How far in advance does it need to apply the brakes? 8. A satellite in space is travelling at 14 m/s in one direction. A thruster is applied for 30 s and the satellite is then travelling at 12 m/s in the opposite direction. What acceleration does the thrust cause? 9. A rock is dropped off a 40 meter cliff. The rock accelerates due to gravity. What is the time it takes to hit the ground? 10. A motorcycle is travelling at a constant velocity of 90 km/h (no acceleration). How many seconds will it take the motorcycle to cover 2 km? BOL 2019 Page 13 of 17 PHYSICS 12 WCLN.ca 11. Hikers at the bottom of a canyon are facing towards the canyon wall 280.5 meters away. Given that the speed of sound in air is 340 m/s, how long after they should will they hear their echo? 12. A child on a toboggan slides down a snowy hill, accelerating uniformly at 2.8 m/s. When the toboggan passes the first observer, it is travelling with a speed of 1.4 m/s. How fast will it be moving when it passes a second observer, who is 2.5 m downhill from the first observer? Show all work as demonstrated in the lessons. 13. A semi-loaded train travelling at 100 m/s can decelerate at 20 m/s. How far in advance must the brakes be applied to come to a stop? 14. A bike rider accelerates constantly to a velocity of 7.5 m/s during 4.5 s. The bike's distance is 19m. What is the initial velocity of the bike? BOL 2019 Page 14 of 17 BOL 2019 a PHYSICS 12 WCLN.ca 15. Provide a description of a sample situation for each of the graphs below (make sure to recognize each graph as d vs t, v vs t, or a vs t). t t Page 15 of 17 " v F t t PHYSICS 12 WCLN.ca Projectiles Review: 1. A stone is thrown horizontally at 15 m/s from the top of a cliff 44 m high. How far from the base of the cliff does it hit the ground? 2. A stone is thrown horizontally at 15 m/s from the top of a cliff 44 m high. What is the velocity of the rock after 2 seconds? 3. An arrow is shot horizontally from the top of a tower at a speed of 15 m/s, and hits the ground with a speed of 25 m/s. Calculate the height of the tower. 4. A golf ball is struck and leaves the ground at 48 m/s on a 60 degree angle. a. How long will it be in the air before bouncing? BOL 2019 Page 16 of 17 PHYSICS 12 b. How far will the ball travel in the air before the first bounce? WCLN.ca C. Determine the velocity of the ball 2 seconds after it was struck. d. The most common incorrect answer for this question is 22m/s. What has actually been calculated if this is the answer? BOL 2019 Page 17 of 17