1. Chapter 2.1-2.3 Review

2. 1. A car is driven 1500 meters west in 120 seconds. What is the velocity in m/s?

3. v =  x/  t v = 1500 m/120 s v = 12.5 m/s west

4. 2. At a speed of 15 m/s, how far could a dog run in 6 seconds?

5. v =  x/  t 15 m/s =  x/6 s  x = 90 m

6. 3. At a velocity of 15 m/s, how long would it take the dog to run 100 meters?

7. v =  x/  t 15 m/s = 100 m/  t  t = 6.7 s

8. 4. A boat accelerates from rest and reaches a velocity of 60 m/s after a time of 20 seconds. What is the average acceleration?

9. a =  v/  t a = 60/20 a = 3 m/s 2

10. 5. A baseball moving at 30 m/s begins a uniform negative acceleration and comes to a complete stop after 5 seconds. How far does the baseball move while decelerating?

11. x = ½(v + v 0 )t x = ½(0 + 30)5 x = 75 m

12. 6. A rocket starts from rest and accelerates for 8 seconds at a rate of 3.6 m/s 2. (A) What is its speed at the end of the 8 seconds? (B) How far does the rocket travel during the FIRST FOUR SECONDS of the 8 second trip? (C) How far does it travel during the last four seconds of the 8 second trip?

13. (A) v = v 0 + at v = 0 + 3.6(8) v = 28.8 m/s

14. (B) x = v 0 t + ½ at 2 x = 0(4) + ½ 3.6(4) 2 x = 28.8 m

15. (C) x = v 0 t + ½ at 2 x = 14.4(4) + ½ 3.6(4) 2 x = 86.4 m

16. 7. A cat runs from rest, uniformly accelerating at a rate of 2.0 m/s 2. What is the velocity of the cat after she has traveled 15.0 m?

17. v 2 = v 0 2 + 2ax v 2 = 0 2 + 2(2)15 v 2 = 60 v = 7.74 m/s

18. 8. Starting from rest, a ball rolls down an incline at a constant acceleration of 4.00 m/s 2. (A) What is the velocity of the ball after 5 s? (B) How far does the ball roll in 7.0 s?

19. (A) v = v 0 + at v = 4(5) v = 20 m/s

20. (B) x = v 0 t + ½ at 2 x = ½ (4) 7 2 x = 98 m

21. 9. A tricycle rolling 10 m/s undergoes a constant deceleration of 2.0 m/s 2. (A) How long does it take the tricycle to come to a stop? (B) How far does the trike move during this time?

22. (A) v = v 0 + at 0 = 10 + (-2)t t = 5 s

23. (B) x = v 0 t + ½ at 2 x = 10 (5) + ½ (-2)5 2 x = 25 m

24. 10. An object starts from rest and moves with constant acceleration for a distance of 400 m in 9.0 s. What is the acceleration of the object?

25. x = v 0 t + ½ at 2 400 = ½ a(9) 2 a = 9.9 m/s 2

26. 11. A rock is thrown downward with a speed of 7 m/s. (A) If it starts from 150 m above the ground, how long will it be in the air before it strikes the ground? (B) What is the final velocity of the rock?

27. This problem is much easier if you do part B before part A. (B) v 2 = v 0 2 + 2gy v 2 = 7 2 + 2(10)150 v = 55.2 m/s (A) v = v 0 + gt 55.2 = 7 + 10t t = 4.8 s

28. 12. A BB is fired vertically upward with a velocity of 150 m/s. (A) What is the peak height the BB will reach? (B) If the BB falls directly back to earth, how long is it in the air?

29. (A) v 2 = v 0 2 + 2gy 0 2 = 150 2 + 2(-10)y y = 1125 m

30. (B) v = v 0 + gt 0 = 150 + (-10)t t = 15 s 15 x 2 = 30 s

31. 13. A toy car rolls off the top of a building and attains a vertical velocity of 55 m/s. How much time did it take the car to fall?

32. v = v 0 + gt 55 = 0 + 10t t = 5.5 s

33. 14. How far did the toy car in the previous problem fall during the third second?

34. v 2 = v 0 2 + 2gy 30 2 = 20 2 + 2(10)y y = 25 m