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# Kinematics/Free Fall

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1. Kinematics/Free Fall By Dan Gallagher, Stephanie Johnson, Kim Grauf, and Ryan Morton

2. Some Key Terms • Speed • Measures how fast something is moving • Velocity • Speed in a certain direction • Instantaneous • Average • Acceleration • Change of velocity in a given time

3. Free Fall • A state of falling without air resistance (only force is gravity) • Acceleration is –9.8 m/s2 • Use three of the following equations

4. Kinematics • v=d/t • a= (vf-vi)/t • d= ½ at2 + vit • 2ad=vf2-vi2

5. Kinematics Examples • A ball is dropped from 7 m above the ground. How fast is it moving 1.2 seconds later? • -11.76m/s • A rock is dropped from a cliff that is 50 m high. If you throw a ball down from the cliff 2 seconds later so that is reaches the ground at the same time as the rock, how fast must the ball be thrown? • 36.19 m/s

6. a) How long does it take to reach its maximum height? 44.89 seconds b) How fast and in what direction is the bullet moving after 3 seconds? Up at 410.6 m/s More Kinematics Examples A bullet is fired straight up into the air with an initial speed of 440 m/s.

7. 1.) A race car can slow down with an acceleration of –11 m/s2. If the car is going 55 m/s, how many meters will it take to stop? Givens: a = -11 m/s2 vi = 55 m/s vf = 0 m/s d = ? The Quiz! Equation—2ad=vf2-vi2 d=-137.5 meters

8. Givens: a = -9.8 m/s2 t = 8 seconds vf = ? vi = 0 m/s 2.) A stone falls freely form rest for 8.0 seconds. A) What is the final velocity? The Quiz Continues Equation—a=(vf-vi)/t vf=-78.4 m/s

9. B) What distance does the stone fall during this time? Equation—d=1/2at2+vit #2 continued… Givens: d = ? a = -9.8 m/s2 t = 8.0 seconds vi = 0 m/s d = -313.6 meters

10. 3.) You are driving down a street in a car at 55 km/hr. Suddenly a child runs into the street. If it takes you 0.75 seconds to react and apply the brakes, how many meters will you have moved before you begin to slow down? Givens: vf = 96 m/s t = 8 seconds a = ? vi = 32 m/s There’s More?! Equation—a = (vf-vi/)t a = 8 m/s

11. 4.) Determine the final velocity of 22 m/s accelerated uniformly at the rate of 1.6 m/s2 for 6.8 seconds. Givens: t = 6.8 seconds a = 1.6 m/s2 vi = 22 m/s vf = ? Last One! Equation—a=(vf-vi)/t vf = 32.88 m/s

12. Extra Tips for Final • Go over your picket fence/Galileo lab • Go over chapter 2, pgs 10-24 • Worksheet 2-1 + 2-2 • 3 worksheets on Kinematics • Kinematics take home quiz

13. The End!