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Warm-up

10/15 p. 5. Warm-up. 1. Sketch a prediction of a velocity vs. time graph for a freely falling object if you ignore air resistance.

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Warm-up

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  1. 10/15 p. 5 Warm-up 1. Sketch a prediction of a velocity vs. time graph for a freely falling object if you ignore air resistance. 2. You left the cafeteria running initially at 2.7 m/s and accelerated uniformly at a rate of 0.02 m/s2 until you arrived at classroom 3.5 minutes (210 seconds) later. How fast were you running when you arrived to class? Use WTF, circle answer & include units Velocity (m/s) Time (s)

  2. What do these graphs indicate? Speed Time Distance vs. Time Speed vs. Time Speed vs. Time Speed Time

  3. Describing Motion • There are five things we need to know about an object’s motion in order to fully describe it. • v = velocity (initial vs. final) • t = time • d= displacement (vs. distance) • a = acceleration • As long as you know at least 3 of the 4 variables, you can solve for the 4th & the 5th. • These only work in situations where acceleration is constant.

  4. Kinematic Equations*KNOW how to manipulate* • * NO “t” • * NO “Vf” • Vf= Vi + at * NO “d” • Vf2= Vi2 + 2ad * NO “t”

  5. Practice Problems An airplane accelerates down a runway at 3.20 m/s2 for 32.8 s until is finally lifts off the ground. Determine the distance traveled before takeoff. WTF

  6. Feather & Hammer Drop on the Moon http://www.youtube.com/watch?v=5C5_dOEyAfk

  7. A feather is dropped on the moon and hits the surface of the moon 1.29 seconds later. The acceleration of gravity on the moon is 1.67 m/s2. Determine the height the feather was dropped.

  8. A car starts from rest and accelerates uniformly to a speed of 26.0 m/s for a distance of 110 m. Determine the acceleration of the car.

  9. What happens when you drop something? • Gravity pulls the object downward and causes it to accelerate. • The acceleration of gravity is constant: 10 m/s2 • The acceleration of gravity is always downward and constant. • We will always use -10 m/s2

  10. Consider an object thrown straight up • It continues to move upward for a while, then it comes back down. • At the highest point, when the object is changing its direction of motion from upward to downward, its instantaneous speed is zero. • It then starts downward, just as if it had been dropped from rest at that height.

  11. vi(up ) = vf(down) • vf(up) = vi(down ) = 0 • The change in speed each second is the same whether the object is going upward or downward.

  12. Look at one side or the other

  13. Hint • If you are trying to find time up, solve for time down. • If you are trying to find distance up, solve for distance down.

  14. Practice Problems  1. Henrietta is walking through a dark room when she sees a scary animal. She jumps up at a speed of 3.4 m/s. How high does she jump? WTF

  15. Practice Problems 2. Jerry the tomcat wants to jump up onto the refrigerator to reach the cheesy-poofs. If the refrigerator is 2m tall, how fast must Jerry jump to make it?

  16. Practice Problems 3. A bullet is fired straight up with a muzzle velocity of 460 m/s. What is the maximum height the bullet will reach?

  17. Closure Create a up/down motion problem, show your WTF, solve & explain to your neighbor

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