HORIZONTAL PROJECTILE PROJECTED AT M S

Name (printed) _______________________________

First Day Stamp

ACTIVITY

THE MOTION OF PROJECTILES

INTRODUCTION

In this activity you will begin to understand the nature of projectiles by mapping out the paths of two projectiles over time; the first moving horizontally

and the other projected at a 30? angle above the horizontal.

HORIZONTAL PROJECTILE (PROJECTED AT 15 M/S)

1. A rock is thrown horizontally from the top of a cliff. Calculate the horizontal position of the rock after each second (using Equation 1) and place these positions in the table below. Assume the rock is moving horizontally at a constant speed of 15 m/s. Show calculation for t = 3 s here:

2. Calculate the vertical positions of the rock for each second (using Equation 3) and place these positions in the table below. Assume the rock is freefalling from rest. Show calculation for t = 3 s here:

Time (s)

0

1

2

3

4

5

6

Horizontal

0

15

Position (m)

Vertical

0

-4.9

Position (m)

3. Now plot ordered pairs of the horizontal and vertical positions of the rock in the graph below. Connect the dots with a smooth curve in order to see the full path of the rock.

0

-50

-100

Vertical Position (m)

-150

0

50

100

Horizontal Position (m) 1

NON-HORIZONTAL PROJECTILE (PROJECTED AT 39 M/S AND AT AN ANGLE OF 30? ABOVE THE HORIZONTAL)

1. You must first determine the horizontal and vertical components of motion from the projection speed and angle of the rock. Do this here:

2. Calculate the horizontal position of the rock after each second and place these positions in the table below. Show calculation for t = 3 s here:

3. Calculate the vertical positions of the rock for each second and place these positions in the table below. Show calculation for t = 3 s here:

Time (s)

0

1

2

3

4

5

6

Horizontal

0 33.8

Position (m)

Vertical

0 14.6

Position (m)

4. Now plot ordered pairs of the horizontal and vertical positions of the rock in the graph below. Connect the

dots with a smooth curve in order to see the full path of the rock.

20

0

-20

Vertical Position (m)

-40

-60

0

50

100

150

200

Horizontal Position (m)

2

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LABETTE

HORIZONTAL PROJECTILE MOTION

INTRODUCTION

What you've done earlier in this unit will enable you to understand projectile motion and this labette. As long as you understand constant speed and how objects accelerate under the influence of gravity, then you're all set. As mentioned before, all projectiles are always in a state of doing two easy types of motion that are totally independent of each other ? constant speed horizontally and freefall vertically. It means

that dealing with projectiles is no more difficult than other types of motion, just a bit longer, because you have to analyze both the vertical and the horizontal directions of motion separately. This labette will take you through a series of steps in which you deal with both directions of motion and hopefully illustrate their independence.

PRE-LAB PROBLEMS

These must be checked with me before starting the labette.

1. A bully is pickin' on you because he's jealous of your physics ability. You know he's a loser because he uses terms like "day glow" and pronounces nuclear "nuke-you-ler." You tell him he's out of his league and to prove it you claim to know projectile motion so well you can project an old rotten tomato horizontally so that it lands on his shoe, which is a horizontal distance of 15.0 m away. You throw the tomato horizontally at a speed of 23.8 m/s and it's a direct hit! The bully takes off running; your honor is secure. What is the height of the tomato when it leaves your hand?

2. a. A very cool physics party is going on at the roof of a ten-story building when a physics boy begins to choke on a chicken bone. A number of physics girls, who were trying to find a reason to hug the big guy anyway, pretend to give him the Heimlich Maneuver. It works, and the bone goes sailing out horizontally at 35 m above the ground. When the bone strikes the ground 21 m from the base of the building, the girls drop the big lug and dash for napkins in order to calculate the speed of the bone as it was projected from the guy's mouth. Share their excitement and calculate the speed!

3. Two 10-year-old boys are doing dumb things that only 10-year-old boys do. One boy bets the other that he can run horizontally across a rooftop and land safely on the roof of an adjacent building. The horizontal distance between the two buildings is 3.5 m, and the roof of the adjacent building is 2.4 m below the jumping off point. How fast does he have to run in order to make it?

3

PURPOSE

To use the equations of motion and the ideas of projectile motion to predict the range of a horizontal projectile.

PROCEDURE

Fire the projectile launcher vertically into the air several times, measuring the maximum height of the metal ball with a ruler each time.

Trigger Cord ? Pull away from launcher at a 90? angle.

Plumb Line ? Used to measure angle of projection.

DATA

Maximum Height of Ball (m)

Figure 10.5: Projectile Launcher

Horizontal and vertical position of projectile when launched.

Average maximum height of the ball: ________

Height above the ground the ball is launched: _______

QUESTIONS/CALCULATIONS (SHOW ALL WORK)

1. Use the maximum height of the ball to calculate its initial speed.

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2. Now consider launching the ball horizontally from the launcher, with its horizontal speed being the speed calculated above. Set this up as a projectile motion problem and calculate what horizontal range the ball should have. You will also use the height the ball is launched from above the ground in this calculation. (Don't actually shoot it until I come over to check your numbers and watch the shot with you.)

3. Measure the actual horizontal range and calculate the percent error.

4. Calculate the vertical velocity of the ball when it reaches the floor.

5. Now assume that when you were initially firing the launcher straight up that the ball had gone twice as far. Also, assume that when you fire horizontally with this new speed, you do so from the top of your head. Calculate the new horizontal range and final vertical velocity of the ball. (Each partner does this for his or her own height. If you are the same height, have older partner add 5.0 cm to his/her height.)

5

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100% CORRECT

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