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Average speed - distance traveled/elapsed time.

Mechanics - study of motion and forces. Mechanics has two parts: kinematics and dynamics. Kinematics - describes motion without references to forces. (chapters 2 & 3) Dynamics - the effects forces have on motion. (chapter 4).

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Average speed - distance traveled/elapsed time.

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  1. Mechanics - study of motion and forces. Mechanics has two parts: kinematics and dynamics.Kinematics - describes motion without references to forces. (chapters 2 & 3)Dynamics - the effects forces have on motion. (chapter 4)

  2. Displacement - a vector drawn from the initial position to the final position. Usually represented by Δx, measured in meters (m), and may be positive or negative.

  3. Average speed - distance traveled/elapsed time.

  4. Ex. 1 - How far does a jogger run in 1.5 hours if his average speed is 2.22 m/s?

  5. Ex. 2 - With an average speed of 67 m/s, how long does it take a falcon to dive to the ground along a 150-m path?

  6. Average velocitydisplacement / elapsed time, Δx/Δt.

  7. Ex. 3 - A world record for the fastest jet-engine car was set in 1983 at 283 m/s. Two runs are made in opposite directions over the same course to nullify wind effects. The car first travels 604 m in 2.12 s. In the reverse direction it covers 604 m in 2.25 s. Find the average velocity for each run.

  8. Instantaneous velocity - the velocity at an instant in time.Average acceleration - change in velocity / elapsed time, Δv/Δt.Instantaneous acceleration - acceleration at an instant in time.

  9. Ex. 4 - A plane starts from rest at t0 = 0. The plane accelerates down the runway and at t = 29 s attains a velocity of v = +260 km/h, where the plus sign indicates the velocity points to the right. Determine the average acceleration of the plane.

  10. Ex. 5 - A parachute and brakes begin slowing a drag racer at t0 = 9.0 s, the velocity is v0 = +28 m/s. When t = 12.0 s, the velocity has been reduced to v = +13 m/s. What is the average acceleration of the dragster?

  11. Kinematic equationsv = v0 + atx = vt = 1/2 (v0 + v)tx = v0t + 1/2 at2v2 = v02 + 2ax

  12. Ex. 6 - A speedboat has a constant acceleration of +2.0 m/s2. If the initial velocity of the boat is +6.0 m/s, find its displacement after 8.0 seconds.

  13. Ex. 7 - A jet is taking off the deck of an aircraft carrier. Starting from rest, the jet is catapulted with a constant acceleration of +31 m/s2 along a straight line and reaches a velocity of +62 m/s. Find the displacement of the jet.

  14. Ex 10 - A spacecraft is traveling with a velocity of +3250 m/s. Suddenly the retrorockets are fired, and the spacecraft begins to slow with a acceleration whose magnitude is 10.0 m/s2. What is the velocity of the spacecraft when the displacement of the craft is +215 km, relative to the point where the retrorockets began firing?

  15. Ex 11 - A woman is running at a constant velocity of +5.0 m/s in an attempt to catch a stationary bus. When she is 11 m from the bus, it pulls away with a constant acceleration of +1.0 m/s2. From this point, how much time does it take her to reach the bus if she keeps running with the same velocity?

  16. Ex 12 - A motorcycle, starting from rest, has an acceleration of +2.6 m/s2. After the motorcycle has traveled a distance of 120 m, it slows down with an acceleration of -1.5 m/s2 until its velocity is +12 m/s. What is the total displacement of the motorcycle?

  17. Reasoning Strategy - 1) Construct a drawing to represent the situation.2) Decide which directions are positive and negative.3) Write down the values that are given and the unknown.4) Find the kinematic equations that apply.5) The final velocity of one segment is the initial velocity for the next.6) Remember there may be two possible solutions.

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