Name ______Period ____
Physics (UNIT 4) REVIEW ! -> PROJECTILES & UCM
1. A vector is a quantity that has ______.
a. magnitude and timeb. magnitude and directionc. time and direction
2. A scalar is a quantity that has ______.
a. magnitudeb. timec. directiond. color
3. When representing velocity as a vector ______.
a. the length of the arrow represents the speed.
b. the length of the arrow is drawn to a suitable scale.
c. the direction of the arrow shows the direction of the motion.
d. all of the above.
e. none of the above.
4. The horizontal component of a projectile’s velocity is independent of ______.
a. the vertical component of its velocityb. the range of the projectile
c. timed. none of the above
5. In the absence of air resistance, the vertical component of a projectile’s velocity does not change as the projectile moves.
a. always trueb. sometimes truec. always false
6. In the absence of air resistance, the horizontal component of a projectile’s velocity does not change as the projectile moves.
a. always trueb. sometimes truec. always false
7. At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height. Which ball hits the ground first?
a. the horizontally thrown ball
b. the dropped ball
c. neither---They hit the ground at the same time.
8. A ball is thrown into the air at some angle. At the very top of the ball’s path, its velocity is ______.
a. entirely verticalb. entirely horizontal
c. both vertical and horizontald. cannot be determined
9. At what part of a path does a pitched softball have minimum (zero) vertical speed?
a. just after it is thrownc. at the top of the path
b. halfway to the topd. when it returns to the glove
10. A cannonball is launched horizontally from a tower. If the cannon has a barrel velocity of 100 m/s, where will the cannonball be 1 second later? (Neglect air resistance.)
a. 50 m downrangeb. 98 m downrange
c. 100 m downranged. 490 m downrange
JUSTIFY THE ANSWER ABOVEWITH THE GUESS METHOD and A FREE BODY DIAGRAM.
Given: VI = 100 m/s t = 1 s
Unknown: horizontal displacement
Equation: ∆ x = VI (t)
Substitute ∆ x = (100 m/s) (1 sec)
Solve ∆x = 100 m
11. After a rock that is thrown straight up reaches the top of its path and is starting to fall back down, its acceleration is (neglecting air resistance) ______.
a. greater than when it was at the top of its path
b. less than when it was at the top of its path
c. the same as when it was at the top of its path
12. Which choice most accurately describes the motion of an object projected horizontally from a height?
a. vertical speed increases uniformly; horizontal speed increases uniformly
b. vertical speed increases uniformly; horizontal speed is constant
c. vertical speed constant; horizontal speed decreases uniformly
d. vertical speed constantly changes; horizontal speed is constant
13. An object is projected horizontally from a height. The horizontal displacement
a. is constant
b. decreases uniformly with time
c. increases uniformly with time
d. increases as the square of time
14. Which of the following is an example of projectile motion?
a. a helicopter hovering
b. a softball once pitched
c. a spitwad shot at the teacher
d. a rock falling to Earth
15. If a rock is thrown horizontally from the same height and at the same time another rock is dropped, which will hit the ground first?
a. the thrown rock
b. the dropped rock
c. neither
16. Harry accidentally falls off of his broom which is traveling horizontally at 15 m/s. He plunges into the water below him 2.0 seconds later. Assuming no air resistance, what is the horizontal distance he travels while falling?
DRAW A FREE BODY DIAGRAM AND USE THE GUESS METHOD TO SOLVE.
Given: VI = 15 m/s t = 2 s
Unknown: horizontal displacement
Equation: ∆ x = VI (t)
Substitute ∆ x = 15 m/s (2 sec)
Solve ∆x = 30 m
17. An object is projected horizontally at 7.0 m/s from the top of a 44 m cliff. How far from the base of the cliff will the object strike the ground?
DRAW A FREE BODY DIAGRAM AND USE THE GUESS METHOD TO SOLVE.
Given: VI = 7.0 m/s height = 44 m
Unknown: horizontal displacement (must find time first)
Equation: ∆ y = (1/2) a (t)2 Remember, a = 10 m/s2 because of gravity since this vertical.
Substitute 44 m = (1/2) (10 m/s2) t2
8.8 = t2
Solve 3.0 s = t (rounded)
Equation: ∆ x = VI (t)
Substitute ∆ x = 7.0 m/s (3.0 sec)
Solve ∆x = 21 m
18. A bullet traveling 250 m/s horizontally hits a target 500 m away. How far does the bullet fall before it hits the target? DRAW A FREE BODY DIGRAM AND USE THE GUESS METHOD TO SOLVE.
Given: VI = 250 m/s horizontal displacement = 500 m
Unknown: vertical displacement (must find time first)
Equation: ∆ x = VI (t)
Substitute 500 m = 250 m/s (t)
Solve t= 2 s
Equation: ∆ y = (1/2) a (t)2 Remember, a = 10 m/s2 because of gravity since this vertical.
Substitute ∆ y = (1/2) (10 m/s2) (2 sec)2
Solve ∆y = 20 m
19. A rock is thrown with a horizontal velocity of 15 m/s takes 8 seconds to hit the ground. What is the height of the cliff? How far does the rock land from the edge of the cliff when it hits the ground?
DRAW A FREE BODY DIGRAM AND USE THE GUESS METHOD TO SOLVE.
Given: VI = 15 m/s time = 8 sec
Unknown: vertical displacement, horizontal displacement
Equation: ∆ y = (1/2) a (t)2 Remember, a = 10 m/s2 because of gravity since this vertical.
Substitute ∆ y = (1/2) (10 m/s2) (8 sec)2
Solve ∆ y = 320 m
Equation: ∆ x = VI (t)
Substitute ∆ x = 15 m/s (8 s)
Solve ∆ x= 120 m
20. An airplane drops supplies as a reward to tribe members of the showSurvivor: Gabon. You are one of the tribe, watching on the ground as the plane flies past you. (Neglect air resistance.) You see the box of supplies land:
- ahead of the airplane
- behind the airplane
- directly below the airplane
- nowhere because it was voted off
21. The cannonball with a horizontal velocity component to the right of 15 m/s would simply look like an object in free fall to an outside observer if the observer’s frame of reference:
A. accelerates at 9.8 m/s2 upC. moves right at 15 m/s
B. accelerates at 9.8 m/s2 downD. moves left at 15 m/s
22. You are standing on a train platform waiting for your train to arrive. A train traveling 30 m/s east passes by with the Three Stooges on it. Curly (who is standing on the train) is throwing pies 3 m/s east at Moe (who is standing on thetrain). DRAW A PICTURE OF THIS EVENT. USE THE PICTURE TO ANSWER THE NEXT 5 QUESTIONS.
How fast is the train moving relative to you? ______30 m/s east___
How fast is the pie moving relative to you? ______33 m/s east___
How fast is Curly moving relative to you? ______30 m/s east______
How fast is the pie moving relative to Curly? ______3 m/s east______
How fast is Moe moving relative to Curly? ______0 m/s ______
23. In a physics lab, a 10 g marble, after rolling down a ramp, shoots off the edge of a table with a horizontal velocity of 1.2 m/s. The table is 1.0 m high. You want the marble to land in a shallow cup on the floor. How far from the edge of the table should you place the cup? DRAW A FREE BODY DIGRAM AND USE THE GUESS METHOD TO SOLVE.
Given: VI = 1.2 m/s height = 1 m
Unknown: horizontal displacement (must find time first)
Equation: ∆ y = (1/2) a (t)2 Remember, a = 10 m/s2 because of gravity since this vertical.
Substitute 1 m = (1/2) (10 m/s2) t2
.2 = t2
Solve .45 s = t (rounded)
Equation: ∆ x = VI (t)
Substitute ∆ x = 1.2 m/s (.45 s)
Solve ∆x = .54 m
24. Why does the mass of the marble (in the question above) doesn’t matter in figuring the horizontal displacement?
The only components needed to find horizontal displacement of a projectile is the initial velocity (which is constant) and the time needed for the object to hit the ground.