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Warm Up 1. Describe the motion of the person. 2. Find the velocity of the person at each interval.
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Warm Up 1. Describe the motion of the person. Stands still, moves away, stands still, moves toward 1. Find the velocity of the person at each interval. 0 m/s, 0.4 m/s, 0 m/s, 0.25 m/s
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Change in Velocity Initial Velocity (v i ) – An object’s velocity when you start measuring acceleration Final Velocity (v f ) – An object’s velocity when you finish measuring acceleration Δv = v f - v i
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Acceleration
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Quick Checks What is acceleration? Is there acceleration in these situations? Why? a) A car stopping at a red light b) A car using cruise control on the freeway. c) A pendulum d) Dropping an egg – Answers on next click
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Quick Checks What is acceleration? Is there acceleration in these situations? Why? a) A car stopping at a red light b) A car using cruise control on the freeway. c) A pendulum d) Dropping an egg
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Acceleration Acceleration is not just a change in velocity, it’s how fast that change happens.
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Units for Acceleration
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Acceleration Positive acceleration = speeding up Negative acceleration = slowing down
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Practice – Ex 1 A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?
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Use GUESS! G: v f = 26 m/s v i = 10 m/s ∆t = 2 s U: acceleration E: acceleration = ∆v/∆t S: a = 26m/s – 10m/s 2 s S: a = 16m/s 2s a = 8m/s/s or 8m/s 2 A roller coaster’s velocity at the top of a hill is 10m/s. Two seconds later it reaches the bottom of the hill with a velocity of 26m/s. What is the acceleration of the roller coaster?
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Quick Checks 1. A car travels in a straight line at 60 mi/hr. A. Is the car accelerating? B. What is the car’s acceleration? 2. A car goes from 0 mph to 60 mph in 6 seconds. A. Is the car accelerating? B. What is the car’s acceleration? Answers on next slide
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Quick Checks 1. A car travels in a straight line at 60 mi/hr. A. Is the car accelerating? No B. What is the car’s acceleration?0 m/s 2 2. A car goes from 0 mph to 60 mph in 6 seconds. A. Is the car accelerating? Yes B. What is the car’s acceleration? (60 – 0 mph)/6 s = 60 mph/6s = 10 miles /hr · s
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Practice Problems- Use GUESS a) While traveling along a highway a driver slows from 25 m/s to 15 m/s in 12 seconds. What is the automobile’s acceleration? (Remember that a negative value indicates a slowing down or deceleration.) b) While hunting a gazelle, a lion starts from rest, and speeds up to 20 m/s in 4.2 seconds. What is the acceleration of the lion?
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Example 2 If a Ferrari, with an initial velocity of 10 m/s, accelerates at a rate of 50 m/s 2 for 3 seconds, what would its final velocity be?
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Practice – Use GUESS In a car accident, a driver hits the brakes to decelerate at 3 m/s 2 in 2 seconds. What speed was the car going before the accident, assuming it comes to a complete stop? G: a = -3 m/s 2 t = 2 sec v f = 0 m/s
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Homework Speed, Velocity, Acceleration Work Sheet
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Exit Question What is the final velocity of a car that starts at 10 m/s, then accelerates at 5 m/s/s for 10 seconds? USE GUESS!!
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