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- (15 pts) It is a simple modification to put a 24 mm diameter motor mount in an Estes Baby Bertha rather than the 18 mm diameter mount that comes with the kit. This allows use of substantially larger motors, such as the Aerotech F24.
a) If 1 lb = 4.448 N, list the average thrust of the F24 rocket motor in both Newtons and pounds.
Since the number following the letter in the motor designation is the average thrust in Newtons, the average thrust of an F24 is 24 N.
24 N ×
1 lb 4 .448 N
= 5.4 lb
b) If a Baby Bertha has a mass of 44.5 g when ready to launch (but without the motor installed) and the F24 has a total mass of 62.2 g before firing (including propellant and casing), what is the weight of the rocket and motor together (in pounds)? Note that 1 kg of mass has a weight of 9.8 N on earth.
44 .5 g rocket + 62.2 g motor = 106.7 g total
106 .7 g ×
1 kg 1000 g
×
9 .8 N
1 kg
×
1 lb 4 .448 N
= 0.235 lb
c) The F24 motor has a total impulse of 50 N·s and propellant mass of 19 g. Is the Baby Bertha, flown with an F24, legally classified as a “model rocket”?
- It weighs less than one pound.
- There is less than 4 oz propellant (1 oz. is 28.3 g).
- The motor has less than 80 N average thrust.
- The motor has less than 160 N·s impulse.
Therefore, this is a “model rocket.”
- (20 pts)
a) When the cathode ray tube experiment was carried out, what results lead to the conclusion that the “pieces” of electricity were found in all types of elements?
The same results were observed no matter what material was used for the anode and cathode. Thus it was surmized that the same electricity particles must be in all these different types of materials.
b) Explain what is wrong with the figure of an atom shown below.
Nucleus
Electrons
While electrons do exist around the nucleus, they do not orbit the nucleus in the manner shown in the diagram.
- (20 pts)
a) What must happen to a solid fuel before it can combust. You may use combustion of any solid fuel as an example, including candle wax, the solid fuel in a hybrid rocket motor, or even the solid propellant in a solid rocket motor.
Before a solid fuel can combust, it must first be vaporized and then pyrolized. In a candle, energy from the flame melts and then vaporizes the wax. The hydrocarbons in the vaporized wax are then pyrolized (cracked) into smaller pieces which can then combust.
b) What are some things you can do to stop a combustion reaction?
- Remove the fuel.
- Remove the oxidizer.
- Remove the energy source.
Any of the above items will cause the combustion reaction to stop.
- (20 pts) An engineer working on a new rocket fuel brings you, as the project director, the chemical reaction that he has worked out:
2 H 8 C 7 + 6 N O 3 → 2 C 7 H 5 N 3 O 6 + 3 H 2 O
a) Identify the atoms by chemical symbol and common name that are involved in this reaction? (You do not need to identify the four molecules in the equation.)
- H → hydrogen
- C → carbon
- N → nitrogen
- O → oxygen
b) Did the engineer correctly balance the equation? Explain.
Element Left Right H 16 16 C 14 14 N 6 6 O 18 16
Since there is not the same number of oxygen atoms on both sides of the equation, it is not correctly balanced.
