Acceleration review. Regular

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1 Acceleration review Regular

2 Book pg 82 #91 A car is traveling 20m/s when the driver sees a child standing on the road. She takes 0.80s to react, then steps on the brakes and slows at 7.0m/s 2. How far does the car go before she applies brakes? (part 1 of the question) List Givens/unknowns Vi = 20m/s t= 0.80s a = -7.0 m/s2 X =? Δx = vi*t + ½ *a*t 2 Δx = (20)(0.80) + 0.5(-7.0)(0.80) 2 Δx = Δx =13.76 (reaction time only)

3 Book pg 82 #91 A car is traveling 20m/s when the driver sees a child standing on the road. She takes 0.80s to react, then steps on the brakes and slows at 7.0m/s 2. How far does the car go before it stops?(part 2 of the question) List Givens/unknowns Vi = 20m/s t= 0.80s a = 7.0 m/s 2 X =? Vf = 0m/s Vf 2 = vi 2 + 2ad 0 = (20) 2 +2(7)d 0 = d -400/14 = d d = (once brakes applied) =

4 Book pg 82 #98 A stone that starts at rest is in free fall for 8.0s? A. Calculate the stone s velocity after 8.0s List Givens/unknowns Vi = 0m/s t= 8.0s Vf = vi + at a = 9.8 m/s 2 vf = 0 + (9.8)(8) Vf =? Vf = 78.4

5 Book pg 82 #98 A stone that starts at rest is in free fall for 8.0s? B. What is the stone s displacement during this time? List Givens/unknowns Vi = 0m/s t= 8.0s Vf 2 = vi 2 + 2ad a = 9.8 m/s 2 (78.4) 2 = (9.8) d Vf = 78.4 X =? d = m

6 Problem 1 An airplane is waiting in line to take off. It then accelerates down a runway at 3.20 m/s 2 for 32.8 s until it finally lifts off the ground. Determine the distance traveled before takeoff. What is the acceleration? 3.20 m/s 2

7 Problem 1 An airplane is waiting in line to take off. It then accelerates down a runway at 3.20 m/s 2 for 32.8 s until it finally lifts off the ground. Determine the distance traveled before takeoff. Make a list of your givens/unknowns Given: a = +3.2 m/s 2 t = 32.8 s vi = 0 m/s Δx =?

8 Problem 1 An airplane is waiting in line to take off. It then accelerates down a runway at 3.20 m/s 2 for 32.8 s until it finally lifts off the ground. Determine the distance traveled before takeoff. What equation would you use to solve for distance? Δx = vi*t + ½ *a*t 2

9 Problem 1 An airplane is waiting in line to take off. It then accelerates down a runway at 3.20 m/s 2 for 32.8 s until it finally lifts off the ground. Determine the distance traveled before takeoff. Given: a = +3.2 m/s 2 t = 32.8 s vi = 0 m/s Δx =? Δx = vi*t + 0.5*a*t 2 Δx = (0 m/s)*(32.8 s)+ 0.5*(3.20 m/s 2 )*(32.8 s) 2 Δx = m

10 Problem 2 A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car. What is the initial velocity? 0 m/s

11 Problem 2 A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car. Make a list of your givens/unknowns Given: Δx = 110 m t = 5.21 s vi = 0 m/s a =?

12 Problem 2 A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car. What equation would you use to solve for acceleration? Δx = vi*t + ½ *a*t 2

13 Problem 2 A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car. Given: Δx = 110 m t = 5.21 s vi = 0 m/s a =? Δx = vi*t + 0.5*a*t m = (0 m/s)*(5.21 s)+ 0.5*(a)*(5.21 s) m = (13.57 s 2 )*a a = (110 m)/(13.57 s 2 ) a = 8.10 m/s 2

14 Problem 3 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car. What is the initial velocity? 18.5 m/s

15 Problem 3 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car. Make a list of your givens/unknowns Given: vi = 18.5 m/s vf = 46.1 m/s t = 2.47 s a =??

16 Problem 3 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car. What equation would you use to solve for acceleration? a = (Δ v)/t

17 Problem 3 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the acceleration of the car. Given: vi = 18.5 m/s vf = 46.1 m/s t = 2.47 s a =?? a = (Δ v)/t a = (46.1 m/s m/s)/(2.47 s) a = m/s 2

18 Problem 3 Part 2 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the distance traveled by the car. What equation would you use to solve for distance? Δx = vi*t + ½ *a*t 2 or vf 2 = vi 2 + 2*a*Δx

19 Problem 3 Part 2 A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds. Determine the distance traveled by the car. Given: vi = 18.5 m/s vf = 46.1 m/s t = 2.47 s Δx =?? a = m/s 2 d = vi*t + 0.5*a*t 2 d = (18.5m/s)*(2.47s)+ 0.5*(11.2 m/s 2 ) *(2.47s) 2 d = m m d = m (Note: can use vf 2 = vi 2 + 2*a*d)

20 Problem 4 A stone is dropped into a deep well and is heard to hit the water 3.41 s after being dropped. Determine the depth of the well. What is the rate of acceleration for all free falling objects on earth? 9.8 m/s2

21 Problem 4 A stone is dropped into a deep well and is heard to hit the water 3.41 s after being dropped. Determine the depth of the well. Make a list of your givens/unknowns Given: a = -9.8 m/s2 t = 3.41 s vi = 0 m/s Δx =??

22 Problem 4 A stone is dropped into a deep well and is heard to hit the water 3.41 s after being dropped. Determine the depth of the well. What equation would you use to solve for distance? Δx = vi*t + ½ *a*t 2

23 Problem 4 A stone is dropped into a deep well and is heard to hit the water 3.41 s after being dropped. Determine the depth of the well. Given: a = -9.8 m/s2 t = 3.41 s vi = 0 m/s Δx =?? Δx = vi*t + 0.5*a*t 2 Δx = (0 m/s)*(3.41 s)+ 0.5*(-9.8 m/s 2 )*(3.41 s) 2 Δx = 0 m+ 0.5*(-9.8 m/s 2 )*(11.63 s 2 ) Δx = m (NOTE: the - sign indicates direction)

24 Problem 5 A baseball is popped straight up and is in the air for 6.25 s. Determine the initial velocity with which it was thrown. How much time does it take to reach the maximum height? 3.125s

25 Problem 5 A baseball is popped straight up and is in the air for 6.25 s. Determine the initial velocity with which it was thrown. What equation would you use to solve for initial velocity? vf 2 = vi 2 + 2*a*d

26 Problem 5 A baseball is popped straight up and is in the air for 6.25 s. Determine the initial velocity with which it was thrown. Given: a = -9.8 m/s2 vf = 0 m/s t = 3.13 s vi =?? Vf = vi + at 0m/s = vi + (-9.8)(3.13) 0m/s = vi m/s vi = m/s

27 Problem 5 part 2 A baseball is popped straight up and is in the air for 6.25 s. Determine the maximum height to which the ball rises. What equation would you use to solve for height? vf 2 = vi 2 + 2*a*d

28 Problem 5 Part 2 A baseball is popped straight up and is in the air for 6.25 s. Determine the height to which the ball rises before it reaches its peak. Given: a = -9.8 m/s2 vf = 0 m/s t = 3.13 s Δx =?? vi = m/s Step 2: vf 2 = vi 2 + 2*a*d (0 m/s) 2 = (30.6 m/s) 2 + 2*(-9.8 m/s 2 )*(d) 0 m/s 2 = ( m/s) + (-19.6 m/s 2 )*d m/s = (-19.6 m/s 2 )*d ( m/s)/(-19.6 m/s 2 ) = d d = m

CHAPTER 3 ACCELERATED MOTION

Physics Approximate Timeline Students are expected to keep up with class work when absent. CHAPTER 3 ACCELERATED MOTION Day Plans for the day Assignments for the day 1 3.1 Acceleration o Changing Velocity