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Challenge Problem

Day 1. Challenge Problem. An asteroid charges towards the earth at a velocity of 90,000 km/hr. If the earth is 6.48 x 10 6 km away, how many hours do we have left before the asteroid impacts the atmosphere?. Hint: The formula is v = ∆d/∆t. MOTION!. Three important variables d - distance

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Challenge Problem

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  1. Day 1 Challenge Problem An asteroid charges towards the earth at a velocity of 90,000 km/hr. If the earth is 6.48 x 106 km away, how many hours do we have left before the asteroid impacts the atmosphere? Hint: The formula is v = ∆d/∆t.

  2. MOTION! • Three important variables • d - distance • v - velocity • a - acceleration

  3. Distance vs. Displacement • Distance is the total amount traveled • Displacement is the distance (and direction) from your starting point.

  4. Scalar vs. Vector • A scalar quantity only measures magnitude or value • A vector quantity measures both magnitude and direction • In the real world, moving objects have a direction, so we have to record that as well!

  5. Scalar vs Vector • The value of direction is determined by the sign. Positive or Negative. • Positive – when motion is away from the start point, up, right, east or north • Negative – when motion is toward the starting point, down, left, west or south

  6. Challenge Question • A rag-tag team of astronauts are sent to intercept the asteroid before it hits earth. Their ship travels with an average velocity of 8000 m/s. They are scheduled to contact the asteroid in half an hour. What is their displacement for this time period? Hint: 30 minutes = 1800 seconds Formula: v=∆d/∆t

  7. Day 2 Write these definitions in your physics notebook: Motion: A change in position over a period of time. Position: The location of an object with respect to a reference point Displacement: The distance and direction between two positions, a vector quantity. Distance: The amount traveled between two positions, a scalar quantity. Scalar Quantity: a quantity represented only by magnitude Vector Quantity: a quantity represented by magnitude and direction

  8. Velocity • Velocity is a vector quantity that represents the change in position over an interval of time. • Two types of velocity: Average Velocity and Instantaneous Velocity

  9. Practice problem • You woke up late and need to get to school! You have 10 minutes to drive to campus, and live 15 km away. What must your average velocity be in order to make it to school on time?

  10. Practice Problem • Find the Instantaneous Velocity at each indicated point on the graph. 3 2 4 1 0 m/s 1.11 m/s 0 m/s -1.77 m/s v1 = v2 = v3 = v4 = At point 2: ∆d = 5m and ∆t = 4.5 s At point 4: ∆d = -8m and ∆t = 4.5 s

  11. Ernie went to see some friends in San Antonio 240 miles west. It took him 3 hours to get there from Houston. What was his average speed (in mi/h)? What was his velocity (in mi/h)? In training for the Marathon, Rhonda would run 13 miles due north to the Community Center, where she would meet her friend and swim after her run. If Rhonda ran this in 2 hours, what was her velocity? What was her displacement from home?

  12. Day 3 Challenge Problem! A car commercial claims a Porsche 911 can travel from 0 to 60 mph in 5 seconds. What is the acceleration during this time? Use your STAAR chart to find the correct formula!

  13. Acceleration! • Acceleration is the change in velocity over time. • Formula: a = (vf-vi)/ Δt • Units: distance / time2

  14. Acceleration! • Acceleration is what happens when a Force is applied to an object. (F=ma) • The direction of acceleration follows the direction of that Force (i.e. gravity)

  15. Practice! Use: a = (vf-vi)/ Δt 3. What is the acceleration of a racing car if its speed changes from 44 m/s to 66 m/s in 11 seconds? 4. A train moving at a speed of 45 m/s slows to 15 m/s in 12 seconds. What is its acceleration? • A plane starting from rest accelerates to its take-off speed of 72 m/s during a 5-second period. What is its acceleration?

  16. Free Fall • An object is in free fall whenever the only force acting on it is the force of gravity. • Acceleration due to gravity = -9.8m/s2 • An object in free fall can still have an upwards velocity. • Solve using your same kinematic equations!

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