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1Physics
Names_______________________Period____
Rocket Lab
The purpose of this exercise is to build a commercially available model rocket and predict the height to which it will
fly when launched using a standard C6-5 engine. Using principles of physics, including kinematics and Newton’s
Laws of motion, the “theoretical” total height can be calculated with the use of a few given and measured quantities.
We will then go outside on a day with agreeable weather and launch the rockets, using altimeters to obtain an
“experimental” total height. We can then compare the theoretical and experimental quantities using percent error.
There are two types of motion involved here. When the rocket is launched, it starts from rest and accelerates
vertically upward while the fuel is burning (zone 1) – the “time of burn” is a property of the engine, and will
(presumably) be the same for all rockets. In addition, the thrust of the engines will also be the same for all rockets.
When the fuel runs out, the rocket then begins to slow down under the influence of gravity and air resistance (zone
2) until it reaches its highest point, at which time the parachute is ejected and the rocket starts to descend.
We will calculate the theoretical total height by obtaining the displacement for each zone and adding them up.
Zone 1
Zone 2
vi
0
vi
vi2 (same as vF1)
vF
vF1 (calculated)
vF
vF2
d
d1 (calculated)
d
d2 (calculated)
a
a1 (calculated)
a
a2 (calculated)
t
tB (burn time – given)
t
tD (delay time – given)
B
To perform this calculation, you will need to measure or be given several quantities. These are listed below. Some
are given, some you need to measure.
Qty.
Description
Value
mR
Mass of the rocket before the engine is loaded (kg)
mF
Mass of a full rocket engine (kg)
.024
mE
Mass of an empty rocket engine (kg)
.011
FF
Average air friction force (N)
T
Thrust of the C6-5 engine (N)
5.80
tB
Engine time of burn (s)
1.76
tD
Engine time of delay (s)
5.00
g
Acceleration due to gravity (m/s )
B
2
9.80
When your rocket is completely ready to fire (except for the loading of the engine, which I will take care of) you will
need to find its mass in kg.
The average air friction will be provided by the instructor – we have data on most commercially available rocket kits.
Calculations:
1. Find the average mass during zone 1 (while the fuel is burning).
mavg = ______________
2. Now the average weight of the rocket during zone 1.
Wavg = (mavg)g
Wavg = ________________
3. Find the net force on the rocket during zone 1 (ups – downs, since it’s accelerating vertically upward).
ΣFY1 = T – Wavg – FF
ΣFY1 = ______________
4. Find the acceleration of the rocket during zone 1 using Newton’s 2nd Law and the final velocity and distance
traveled in zone 1.
a1 = ________________
vF1 = ________________
d1 = ________________
5. After the engine runs out of fuel, the mass of the rocket is constant. Find the mass and the weight in zone 2.
m2 = mR + mE
m2 = ________________
W2 = m2g
W2 = ________________
6. Find the net force on the rocket during zone 2 (ups – downs, since it’s still vertically upward, but slowing down).
ΣFY2 = – W2 - FF
ΣFY2 = ______________
7. Find the acceleration of the rocket during zone 2 using Newton’s 2nd Law and the distance traveled in zone 2.
a2 = ________________
d2 = ________________
8. Find the total theoretical height by adding the two distances.
HTH = ___________________
When we go outside, we will fire the rockets and obtain an experimental height. A number of people will move a
distance of 100 meters away over the flattest ground we can find (probably the football field). Each will have an
altimeter, which is used to measure an angle of elevation. By centering the sight on the altimeter on the puff of
smoke emitted when the parachute is ejected, we can measure the angle easily. Then we use some trigonometry to
find the experimental height.
Now we can find the experimental height using the formula below.
List the average angle θ for your rocket from class data, and solve for the experimental height HM.
θ = _______________
HM = ___________________
Now list the theoretical height from #8 above.
HTH = ___________________
Calculate the percent error using the standard formula.
% Error = ___________________