Angry Students Physics Lab for Two-Dimensional Projectile Motion

ANGRY STUDENTS PLAN FOR REVENGE – CLASSIFIED DOCUMENT ______

Angry Students—Physics Lab for Two-dimensional Projectile Motion

MISSION To launch water balloons at an angle to target teachers

MATERIALS 1. Water balloon launcher 2. Anchors 3. Meter stick/tape measurer 4. Water 5. Water balloons 6. Protractor

STRATEGY BRIEFING Angry students, armed with Physics knowledge, conspire to exact revenge on their teachers, Angry Bird style! Projectile motion is the name of the game. Will the teachers receive a taste of the subject they have been preaching all semester long?

ttop (___ 0)

Vi V  ______h yi  t f  ______

Vxi  ______x  ______ANGRY STUDENTS PLAN FOR REVENGE – CLASSIFIED DOCUMENT ______

TIME TO REACH TOP OF TRAJECTORY

Vy= V yi + at

0 =Vyi + at top V t = - yi top a V t=2 t = - 2 yi f top a

INITIAL LAUNCH VELOCITY

1 h= V t + at 2 yi 2 1 = 0�t at 2 2 2h � t a

Dx = Vi t Dx � V i 2h a Dx = ______meters h= ______meters ANGRY STUDENTS PLAN FOR REVENGE – CLASSIFIED DOCUMENT ______

CONSTRAINTS (RULES) 1. Launch Method a. Ensure that every launch is pulled back the length of the string 2. Groups of 3-4 students 3. Each group has different launch angles

PROTOCOL

1. Determine initial launch velocity Vi from a horizontal launch a. Measure height of launcher h b. Pull launcher back to reference string length c. Measure Dx in feet and convert to meters

2. Fire Away! (Angled Launch at _____ degrees) a. With your group’s given launch angle, calculate the horizontal and vertical velocity components in m/s b. Calculate the horizontal distance the water balloon is expected to travel in meters and convert to feet c. Ask teacher to position himself at that distance from launcher d. Launch and measure the actual horizontal distance in meters

3. EXTRA CREDIT: Launch at target with horizontal distance known a. Answer Question 4 first b. Measure horizontal distance of the target from the water balloon launcher in meters c. With the calculated initial launch velocity from 2 and measured horizontal distance, calculate the launch angle (from Question 4) d. Launch at this angle and measure the horizontal distance traveled in meters ANGRY STUDENTS PLAN FOR REVENGE – CLASSIFIED DOCUMENT ______

CALCULATIONS (show in boxes)

Part 1: Determine Initial Launch Velocity (Be sure to know whether you will use the angled or horizontal launch method)

Time for balloon to strike ground Initial Launch Speed Distance balloon travels Angled Horizontal Angled Horizontal q Dx [m ] t1+ t 2 2h Dx Dx [deg] t = t = V = V = 2 a i t cosq i t [s ] [s ] m m [s ] [s ]

Part 2: Angled Launch (use Vi from above) q V V= V cos q 2V Dx Dx i xi i ( ) Vyi= V i sin (q ) yi predicted measured Dxmeasured - D x predicted t f = - %error = 100 [deg] m m m g s [ ] a = V t[ m ] [m ] [ ] s [s ] xi f Dxmeasured [s ]

*Last row is for extra credit ANGRY STUDENTS PLAN FOR REVENGE – CLASSIFIED DOCUMENT ______

DEBRIEFING

1. We want to maximize the horizontal distance of the projectile. Which equation is used to determine the required launch angle? What is that angle?

2. If the launch angle is greater than the one in question 1, does the projectile spend more or less time in the air? Is the horizontal velocity greater or lesser?

3. What are the possible errors in this lab?

4. EXTRA CREDIT: Suppose you know how far your target is and your launch speed, but not the angle of launch. What is the equation that

determines the launch angle needed to hit a target that is Dx meters away with an initial launch velocity of Vi ? Give your answer

symbolically in terms of Vi and Dx . Hint: Use the double angle trig identity sin( 2q) = 2sin q cos q