Names:
Date__________________
Catapult
Lab Report
(With Energy)
Teacher Notes
PLEASE NOTE: For your measurements, launch FROM THE FLOOR. Measure from when
the projectile leaves the catapult on the floor, to when it first hits the floor. This probably
works best out in the hallway so your flaming tar does not hit any targets before making it to the
floor.
A. Show a DIAGRAM here of your projectile. Label everything you can. Include all
possible vectors!
Students should show the whole parabolic trajectory and label vectors on their projectiles.
B. MEASUREMENTS:
__________1) How far (horizontally) did your catapult launch the burning tar toward the enemy
castle?
Example: 3.0 m
__________2) How long was the projectile in the air?
Example: 1.4 s
C. CALCULATIONS & QUESTIONS:
NOTE: SHOW ALL FORMULAS, WORK
AND UNITS!!!
Please put ANSWERS IN BLANKS with correct signs and units. Use negative as down,
positive as up.
__________3) a) How much time did the flaming tar spend GOING UP? Half the total time.
For this example,
1.4 s / 2 = 0.7 s
__________ b) How high did it go? y = ½ a t 2
This works because the height is also how
far the ball fell vertically from the highest point. So half the acceleration due to gravity ( ½ X
9.8 m/s2) times the square of half the total time gives the height! For this example: y = ½ (9.8
m/s2)(0.7s)2 = 2.4 m
__________4) What was the initial horizontal velocity of the projectile as it left the catapult?
For this example: vx = x / t = 3.0 m / 1.4 s = vx = 2.1 m/s
__________5) What was the initial vertical velocity of the projectile as it left the catapult?
Since a = vf-vi / t
and final vertical velocity is 0 at top of path, -vi = at
For this example -vi = -9.8 m/s2(0.7s) = -6.86m/s So vy = 6.86 m/s
__________6) DRAW a vector diagram showing your velocities; label vx, vy, and vR. Then
calculate the resultant speed (the magnitude of the velocity) of your projectile.
For this example:
vx = 2.1 m/s
vy = 6.86 m/s
2.12 + 6.862 = vR2
vR = 7.17 m/s
__________7) What was the resultant direction (angle) of your projectile?
For this example, Tan of angle = 6.86 / 2.1 = 3.27
Angle = 73 degrees
__________8) What was the horizontal acceleration after the projectile was fired? (no work
required)
0 m/s
__________9) What was the vertical acceleration after the projectile was fired? (no work
required)
-9.8 m/s2 (acceleration due to gravity is the vertical acceleration for whole trip)
__________10) What was the horizontal speed at the top of the trajectory (ignoring friction)?
(no work required)
For this example, 2.1 m/s (same for the whole trip, ignoring friction)
__________11) What was the vertical speed at the top of the trajectory (ignoring friction)? (no
work required)
0 m/s (gravity slows vertical speed to 0 at which point projectile falls downward)
__________12) What is the mass of your projectile in kg? (Measure this; no work required)
For this example, 50 g or 0.05 kg
__________13) What is the weight of your projectile in N?
Fw = mg For this example = 0.05 kg x 9.8 m/s2 = 0.49 N
__________14) IF your catapult acted on your object for 0.5 seconds, what was the acceleration
of the object DURING the time the catapult was “pushing” it? (Remember it started from rest!)
a = change in velocity / time or vf – vi / t
For this example: 7.1 m/s – 0 m/s / 0.5 s = 14.2 m/s2
__________15) Given the above, what was the net force of the catapult on the ball?
F = ma So for this example: F = 0.05 kg (14.2 m/s2) = 0.71 N
__________16) What is the maximum gravitational potential energy of your projectile?
PE = mgh For this example: 0.05 kg (9.8 m/s2) (2.4 m) = 1.18 J
__________17) What is the maximum vertical kinetic energy of your projectile?
KE = ½ mv2 For this example: 0.5 (0.05 kg) (6.86 m/s)2 = 1.18 J
D. ANALYSIS & ENGINEERING APPLICATIONS:
__________18) a) Who “won” the contest for most accurate catapult ?
Explain why this group’s contraption worked better to hit the target.
b) Which group’s catapult sent the flaming tar the longest range (horizontal
distance)?
Explain why this group’s contraption worked better to launch the projectile a longer distance.
__________19) If given the chance, how would you build your catapult differently with the
SAME materials, and why?
__________20) If given the chance, what DIFFERENT materials and methods would you use
to make your catapult better, and why?
__________21) Describe what method of production your group feels would be the optimal one
for catapults such as these. For example, do you think mass producing them in teams of 2 (such
as the way we did it in class) would be best, or an assembly line, or some other method?
EXPLAIN your reasoning. Also devise an experiment to test this!
__________22) Do a COST analysis for your product (catapult) and method of production.
Make a list of each item per line showing what you would have to purchase and how much it
would cost. * Don’t forget to charge for your time!