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Monday: Pg. 18 or 24(if no room on 18) Match the unit 1. 2. 3. 4. 5. Speed Velocity Distance Displacment time a) b) c) d) e) Pick up the handout Titled, “Physics” when You pick up journal. 4 Hrs 3 Km west m/s - 4 cm/min 12 meters Instructions: Write everything then match. Thursday (pg. 18) • Can an object accelerate but have a negative value (magnitude)? Ex. -3.4 m/s2 Instructions: Answer in a complete sentence/provide an example. Lab analysis 1. How did the speed change over time for each runner? 2. How did the acceleration of each runner compare to each other? 3. Predict what a speed vs time graph would look like with your data. When you begin to graph distance vs time, you will have to renumber your axes. Wednesday: Pg. 24(if no room on 18) Pick up the pumpkin carving contest paper on the table. a) If distance wasn’t measured in the track activity, how could you use acceleration, time and velocity to determine it? Instructions: Write answer in complete sentence or you can use an equation to show how you would solve for it (it is ok to make up numbers for the variables). Graph Analysis 4. Was the prediction you made in #3 correct? 5. Compare the lines for the two runners on your distance vs time graph. 6. Compare the lines for the two runners on your velocity vs time graph. 7. Choose one runner, does his line on the distance vs time graph look the same as his line on the velocity vs time graph? Why or why not? Chp. 2 Section 2 Acceleration RECAP! • Speed is the magnitude of velocity • Velocity must include direction which can be positive or negative • Speed is a scalar quantity and velocity is a vector quantity • Speed has distance and velocity has displacement • A graph can be used to determine if speed/velocity is constant or changing Why are roller coasters so much fun to ride? • It is a combination of fast velocities and changes in velocity, or acceleration. The average acceleration of an object is defined to be the ratio of its change in velocity to the time taken to change the velocity. v aav = t aav = average acceleration; in units of m/s2 ; length/time2 v = change in velocity; in units of m/s; length/ time t = change in time; in units of s; time Velocity and Acceleration • Copy table. We will use it to answer the questions that follows. • If a baseball has zero velocity at some instant, is the acceleration of the baseball necessarily zero at that instant? • If a passenger train is traveling on a straight track with a negative velocity and a positive acceleration, is it speeding up or slowing down? • When Jennifer is out for a ride, she slows down on her bike as she approaches a group of hikers on a trail. Explain how her acceleration can be positive even though her speed is decreasing. Important basic facts when working with acceleration: • If an objects starts from rest, its initial velocity is 0. • If an object stops, its final velocity is 0. • If an objects falls in the air, it is accelerated by gravity at -9.8 m/s2. The slope and shape of the graph describe the object’s motion Draw Graph in Journal You can learn more about distance, displacement, speed, velocity, relative velocity, and acceleration by clicking on these simulation links: link1, link2, link3, link4, link5 KINEMATIC Motion with constant acceleration • When velocity increases by exactly the same amount during each time interval, acceleration is constant; • Constant distance equal constant velocity equal constant accelereation There are many formulas associated with acceleration vf = vi + at No x x = ½ (vf + vi)t No a x = vit + 2 ½at Vf2 = vi2 + 2ax No vf No t Choose the Correct Equation!!!!!!! 2. A plane starting at rest at one end of a runway undergoes a uniform acceleration of 4.8m/s2 for 15s before takeoff. What is its speed at takeoff? How long must the runway be for the plane to be able to take off? A plane starting at rest at one end of a runway undergoes a uniform acceleration of 4.8m/s2 for 15s before takeoff. What is its speed at takeoff? How long must the runway be for the plane to be able to take off? Part A: Given: vi= 0 m/s; t= 15s; a = 4.8m/s2 Formula: vf = vi + a∆t Substitution: vf= 0 + (4.8m/s2)(15s) Answer w/unit: 72.0m/s Part B: Formula: ∆x = vi∆t + ½ a(∆t)2 Substitution: ∆x = 0(15) + ½ (4.8) (152) Answer w/unit: 540. m Answer to #2. Which equation would I use? Use this equation when you want to find the final velocity of a uniformly accelerated object without knowing how long it has been accelerating. A person pushing a stroller starts from rest uniformly accelerating at a rate 0.500m/s1. What is the velocity of the stroller after it has traveled 4.75m? Given: a=0.500m/s2; vi = 0m/s; x= 4.75m Formula: vf2= vi2 + 2a∆x Substitution vf2= 0 + 2(0.500m/s2)(4.75m) Answer w/unit: √4.75 =2.18m/s 1. An aircraft has a landing speed of 83.9m/s. The landing area of an aircraft carrier is 195m long. What is the minimum uniform acceleration required for a safe landing? Given: vi = 83.9m/s; x= 195m; vf=0 Formula: a= vf2-vi2 Substitution: a= -83.92 2(195) 2∆x Answer w/unit: -18.0m/s2 2. An electron is accelerated uniformly from rest in an accelerator at 4.5 x 107 m/s2 over a distance of 95km. Assuming constant acceleration, what is the final velocity of the electron? Given: vi = 0m/s; x= 95000m; a=4.5 x 107 m/s2 Formula: vf2= vi2 + 2a∆x Substitution vf2= 0 + 2(4.5 x 107m/s2)(95000m) Answer w/unit: 2.92 x 106 m/s A cyclist traveling at 5.0 m/s accelerates with an average acceleration of 1.5 m/s2 for 5.2 s. How large is her final velocity? A train traveling at 6.4 m/s accelerates at 0.10 m/s2 over a distance of 100 m. How large is the train’s final velocity? A ball rolls past a mark on an incline at 0.40 m/s. If the ball has an average acceleration of 0.20 m/s2, what is its velocity 3.0 s after it passes the mark? A car initially traveling at 15 m/s accelerates at a constant rate of 4.5 m/s2 over a distance of 45 m. How long does it take the car to cover this distance? A car accelerates from 10.0 m/s to 15.0 m/s in 3.0 s. How far does the car travel? A race car accelerates at 4.5 m/s2 from rest. What is the car’s velocity after it has traveled 35.0 m? vf = vi + at t = time ∆x = ½ (vi+vf)∆t vi = initial velocity ∆x = vit + ½ 2 a(∆t) vf2 = vi2 + 2a∆x ∆x= displacement a = acceleration vf = final velocity