05a Projectile Motion

The Virtual Prof.’s Concept Questions

Concept Questions Projectile Motion (1, 2, 3, 4) In the series of questions that follow, assume that the magnitude of the acceleration of gravity is exactly 10.0 m/s2 and that there is no friction with the air. A bored golfer standing on a flat, horizontal section of the golf course hits a small stone with his club so that the horizontal and vertical components of its velocity as it leaves the ground are 20.0 m/s and 15.0 m/s respectively. ___ 1. When the stone is at the top of its trajectory, its speed is ___ m/s. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 2. When the stone is at the top of its trajectory, the magnitude of its acceleration is ___ m/s2. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 3. The time required for the stone to reach the highest point in its trajectory is ___ s. (A) 0 (B) 0.5 (C) 1.0 (D) 1.5 (E) 2.0 (F) 2.5 (G) 3 (H) 4 (I) 5 (J) some other value ___ 4. The horizontal distance traveled by the stone before it hits the ground is ___ m. (A) 0 (B) 30 (C) 35 (D) 40 (E) 45 (F) 50 (G) 60 (H) 80 (I) 100 (J) some other value (5, 6, 7) A golf ball is hit on a flat horizontal section of the golf course such that it leaves the ground with a velocity the horizontal component of which is 20.0 m/s and the vertical component of which is 30.0 m/s. For the questions that follow, assume that the acceleration of gravity is 10.0 . . . m/s2. ___ 5. When the golf ball is at the highest point in its trajectory, its speed will be ___ m /s. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 40 (I) 50 (J) some other value ___ 6. The time the ball is in the air before it hits the ground is ___ s. (A) 0 (B) 1.0 (C) 2.0 (D) 3.0 (E) 4.0 (F) 5.0 (G) 6.0 (H) 7.0 (I) 8.0 (J) some other value ___ 7. When the golf ball is at the highest point in its trajectory, the magnitude of the horizontal component of its acceleration is ___ m /s2. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 40 (I) 50 (J) some other value (8 - 14) In the series of questions that follow assume that the magnitude of the acceleration of gravity is 10.0 m/s2 and that there is no friction with the air. A soccer player kicks a soccer ball across a horizontal playing field so that the vertical and horizontal components of the velocity of the ball as it leaves the ground are 20.0 m/s and 10.0 m/s respectively. ___ 8. When the ball is at the top of its trajectory, its speed is ___ m/s. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 9. When the ball is at the top of its trajectory, the magnitude of the vertical component of its acceleration is ___ m/s2. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value

© by Glen Terrell, Summer 2000

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The Virtual Prof.’s Concept Questions ___ 10. The time the ball is in the air before it hits the ground is ___ s. (A) 0 (B) 1 (C) 2 (D) 3 (E) 4 (F) 5 (G) 6 (H) 7 (I) 8 (J) some other value ___ 11. When the ball is at the top of its trajectory, the magnitude of the horizontal component of its acceleration is ___ m/s2. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 12. While the soccer ball is rising to the highest point in its trajectory, the average value of the horizontal component of its velocity is ___ m/s. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 13. While the soccer ball is rising to the highest point in its trajectory, the average value of the vertical component of its velocity is ___ m/s. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value ___ 14. The maximum height attained by the ball is ___ m. (A) 0 (B) 5 (C) 10 (D) 15 (E) 20 (F) 25 (G) 30 (H) 35 (I) 40 (J) some other value (15, 16, 17) For this series of questions, assume that g = 10.00 m/s2. A small stone originally at rest is dropped over the edge of a very tall building. ___ 15. During the fourth second of fall, the speed of the stone changes ___m/s. (A) 0 (B) 5.0 (C) 10 (D) 15 (E) 20 (F) 30 (G) some other value ___ 16. During the second second of fall, the average speed of the stone is ___ m/s. (A) 0 (B) 5.0 (C) 10 (D) 15 (E) 20 (F) 30 (G) some other value ___ 17. During the first second of fall, the stone falls a distance of ___m. (A) 0 (B) 5.0 (C) 10 (D) 15 (E) 20 (F) 30 (G) some other value (18, 19) A 1.0 kg brick and a 10 kg concrete block are dropped off the edge of the same building at the same time. Neglecting any air resistance, then as the pieces fall … ___ 18. … the magnitude of the acceleration of the brick is ___ that of the block. (A) equal to (B) less than (C) more than ___ 19. … the magnitude of the net, external force acting on the brick is ___ that acting on the block. (A) equal to (B) less than (C) more than (20 - 23) For this series of questions, assume that g = 10.00 m/s2. One reaches out over the edge of a tall building and throws a stone straight up with an initial speed of 20.0 m/s. ___ 20. The change in speed of the stone during the first second of its motion is ___ the change in its speed during the third second of its motion. (A) equal to (B) less than (C) more than ___ 21. The distance traveled by the stone during the first second is ___ the distance traveled by the stone during the second second. (A) equal to (B) less than (C) more than

© by Glen Terrell, Summer 2000

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The Virtual Prof.’s Concept Questions ___ 22. At the instant the stone is at its maximum altitude, the acceleration of the stone is ___. (A) 0 (B) 10 m/s2 upward (C) 10 m/s2 horizontal (D) 10 m/s2 downward (E) something else ___ 23. The time required for the stone to reach its maximum altitude is ___ sec. (A) 0 (B) 1 (C) more than 1 but less than 2 (D) 2 (E) more than 2 ___ 24. The force which causes a projectile to undergo the motion it experiences is properly described as ___ (you may not have been exposed to all the physics you need to answer this question). (A) constant (B) constant in magnitude but continually changing in direction (C) zero (D) constant in direction but continually changing in magnitude (E) none of the above (25 - 28) A projectile is launched from ground level with speed vo at an angle φo above the horizontal. ___ 25. If vo was increased slightly, the range of the projectile would ___. (A) increase (B) decrease (C) remain constant (D) increase, decrease, or remain constant depending on other information ___ 26. If φo was increased slightly, the time the projectile spends in the air before hitting the ground would ___. (A) increase (B) decrease (C) remain constant (D) increase, decrease, or remain constant depending on other information ___ 27. If vo was increased slightly, the maximum height attained by the projectile would ___. (A) increase (B) decrease (C) remain constant (D) increase, decrease, or remain constant depending on other information ___ 28. If φo was decreased slightly, the range of the projectile would ___. (A) increase (B) decrease (C) remain constant (D) increase, decrease, or remain constant depending on other information (29 - 34) A golfer hits a rock with a golf club such that the rock leaves the horizontal ground with a velocity, vo, which makes an angle φ = 45 ˚ with the horizontal. The velocity of the rock is such that at the time it leaves the ground, the magnitude of its vertical and horizontal components are each 20 m/s. (Neglect air friction, and assume that g = 10.00 m/s2.) ___ 29. When the rock is at its maximum altitude, the magnitude of its velocity will be ___ 20 m/s. (A) equal to (B) less than (C) more than (D) incomparable, without additional information, with ___ 30. When the rock is at its maximum altitude, the magnitude of its acceleration will be ___10 m/s2. (A) equal to (B) less than (C) more than (D) incomparable, without additional information, with ___ 31. The time required for the rock to reach its maximum altitude is ___ sec. (A) 1 (B) 2 (C) 3 (D) 4 (E) some other number ___ 32. The horizontal distance traveled by the rock before it hits the ground is approximately ___ m. (A) 20 (B) 30 (C) 40 (D) 50 (E) 60 (F) 80 (G) 100 (H) some other value

© by Glen Terrell, Summer 2000

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The Virtual Prof.’s Concept Questions ___ 33. If the angle φ was increased slightly the time the rock spends in the air would ___. (A) increase (B) decrease (C) remain constant ___ 34. If the stone was launched with the same speed, vo, but at an angle φ > 45 °, the range of this second stone would be ___ that of the first. (A) equal to (B) less than (C) more than (35 - 38) A bored golfer hits a stone so that it leaves the horizontal ground with a speed vo at an angle φ < 45 ˚. The stone reaches a maximum altitude A, stays in the air a time interval T and hits the ground with speed vf a distance D from the feet of the golfer. ___ 35. If φ was decreased slightly, T would ___. (A) remain constant (B) decrease (C) increase ___ 36. If vo was increased slightly, D would ___. (A) remain constant (B) decrease (C) increase ___ 37. If φ was decreased slightly, vf would ___. (A) remain constant (B) decrease (C) increase ___ 38. If φ was decreased slightly, A would ___. (A) remain constant (B) decrease (C) increase ___ 39 The maximum altitude attained by a projectile is determined by ___ of its initial velocity. (A) only the horizontal component (B) only the vertical component (C) both the horizontal and vertical components (D) neither the horizontal nor the vertical component ___ 40. The range of a projectile fired at an angle φ above the horizontal is determined by ___ of its initial velocity. (A) only the horizontal component (B) only the vertical component (C) both the horizontal and vertical components (D) neither the horizontal nor the vertical component (41 - 45) A good rock thrower takes a 20 gm stone in his left hand and a 40 gm stone in his right hand and simultaneously throws them both with a speed of 15 m/s at an angle of 45 ˚ relative to the horizontal ground. ___ 41. The time required for the 20 gm stone to reach its maximum altitude is ___ than that for the 40 gm stone. (A) equal to (B) less than (C) more than (D) incomparable with ___ 42. The maximum altitude reached by the 20 gm stone is ___ that reached by the 40 gm stone. (A) equal to (B) less than (C) more than (D) incomparable with ___ 43. The work done by the thrower on the 20 gm stone is ___ done on the 40 gm stone. (A) equal to (B) less than (C) more than (D) incomparable with ___ 44. The distance from the thrower's feet at which the 20 gm stone hits the ground is ___ that for the 40 gm stone. (A) equal to (B) less than (C) more than (D) incomparable with ___ 45. The average acceleration experienced by the 20 gm stone while in "flight" is ___ that experienced by the 40 gm stone while in "flight". (A) equal to (B) less than (C) more than (D) incomparable with

© by Glen Terrell, Summer 2000

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The Virtual Prof.’s Concept Questions (46 - 48) A projectile is launched from ground level with speed vo and at an angle φ (> 45 ˚) above the horizontal. ___ 46. If φ was increased slightly, the maximum altitude attained by the projectile would ___ (A) increase (B) decrease (C) remain constant ___ 47. If φ was increased slightly, the range of the projectile would ___. (A) increase (B) decrease (C) remain constant ___ 48. If vo was decreased slightly, the time required for the projectile to reach its maximum altitude would ___. (A) increase (B) decrease (C) remain constant

KEY 1

E

18

A

35

B

2

C

19

B

36

C

3

D

20

A

37

A

4

G

21

C

38

B

5

E

22

D

39

B

6

G

23

D

40

C

7

A

24

A

41

A

8

C

25

A

42

A

9

C

26

A

43

B

10

E

27

A

44

A

11

A

28

D

45

A

12

C

29

A

46

A

13

C

30

A

47

B

14

E

31

B

48

B

15

C

32

F

16

D

33

A

17

B

34

B

© by Glen Terrell, Summer 2000

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