# Bob

### The rocket equation?

I’m a bit stuck on this simple question.

So the values I’ve got:

Propellant = 100,000 kg

Structure = 10,000 kg

Payload = 5000 kg

So I worked out:

Propellant fraction is 87%

Payload fraction is 4.3%

Now I need to find

“Recall the relationship between specific impulse and exhaust velocity is given by V=gI (Where g = 9.81 and I = 450). What is the change in Velocity (V)in m/s this rocket will produce if all the propellant is consumed in one stage?”

I have tried to work this out and arrived at 1436 m\s but I don’t think I am correct.

Any advice?

Many thanks

1 AnswerMathematics2 months ago### How do I format an equation with conditions for wolfram alpha?

I just want to use wolfram alpha to produce a graph, or symbol lab for double checking. But im not sure the syntax to use.

1 AnswerMathematics4 months ago### Equations of motion?

2 AnswersMathematics9 months ago### Python coding, email checking and filtering.?

Good morning everyone,

I have a really simple project but im very new to python so will need some help if anyone can.

So I want to make a script to check an email account every hour at least and if a message is received with a particular subject I would like to open a file/picture.

Now I have figured out the opening of the file/picture by using webbrowser:

import webbrowser

webbrowser.open('/home/pi/Desktop/PIC.jpg')

But I am not sure how to begin with a script to check an email account (specifically GMAIL) for a message and then if the condition is met to run the code above.

Can anyone help a newbie out?

To add I have been working with the following code to check the emails:

import poplib

from email import parser

pop_conn = poplib.POP3_SSL('pop.gmail.com')

pop_conn.user('USERNAME')

pop_conn.pass_('PASSWORD')

#Get messages from server:

messages = [pop_conn.retr(i) for i in range(1, len(pop_conn.list()[1]) + 1)]

# Concat message pieces:

messages = ["\n".join(mssg[1]) for mssg in messages]

#Parse message intom an email object:

messages = [parser.Parser().parsestr(mssg) for mssg in messages]

for message in messages:

print message['subject']

pop_conn.quit()

But im confused as to where I would put the subject condition, so if I want the email with any subject which contains 'Bananas are the greatest nut' what would I do next?

1 AnswerProgramming & Design2 years ago### Fermi Energy?

Copper has a Fermi energy of 7.02 eV. What is its electron number

density?

----------------------

Using Ef=h^2/8m(3n/pi)^2/3

I get an answer of 2.246*10^7 but this is incorrect. I know the answer is 1.8*10^29 but am struggling to see where I went wrong. Can anyone help?

2 AnswersPhysics2 years ago### Physics, mechanics.?

A swimmer launches himself upwards from a springboard 5.0 m above

the surface of the water in a swimming pool. His trajectory is (almost) vertical, and from the top of his trajectory he passes the springboard in just half of the time he takes to reach the water. How high above the springboard does he rise?

1 AnswerPhysics2 years ago### Physics, Diamonds.?

If enough energy were supplied to a diamond would that allow some of its electrons to transition to a higher energy band and therefore conduct electricity? Just curious.

2 AnswersPhysics2 years ago### Basic physics.?

A man stands on the edge of a cliff with hands outstretched horizontally

carrying two stones, one in each hand. At time

t= 0, he drops the first pebble from rest. After a time of 1.0 s, he releases the second pebble. At what time will the separation between the pebbles be 66 m?

3 AnswersPhysics2 years ago### Physics, isothermal process.?

A sample of 8.02×10^−1 moles of nitrogen gas (γ =1 .40) occupies a volume of 2.00×10^−2 m^3 at a pressure of 1.00×10^5 Pa and temperature of 300K. The sample is isothermally compressed to exactly half its original volume. Nitrogen behaves as an ideal gas under these conditions.

(i)Find the change in entropy of the gas. (ii) What is the change in internal energy of the gas?

(iii) What is the amount of heat transferred from the gas to its environment?

(iv) Calculate the amount of work done in compressing the gas

1 AnswerPhysics2 years ago### Physics. Calculate the temperature and pressure of a Gas.?

A sealed container of volume V =0 .10m^3 holds a sample of N =3 .0×10^24 atoms of helium gas in equilibrium. The distribution of speeds of the helium atoms shows a peak at 1.1×10^3 ms^−1.

(i) Calculate the temperature and pressure of the helium gas.

(ii) What is the average kinetic energy of the helium atoms?

(iii) What is the energy corresponding to the maximum in the energy distribution

1 AnswerPhysics2 years ago### Physics, Electric Potential.?

A uniform electric ﬁeld of magnitude 1.0×10^2 NC^−1 exists between two conducting plates, one of which is positively charged and the other of which is negatively charged. The plates are 10 mm apart.

(a) Calculate the magnitude of the potential diﬀerence between the plates.

(b) If a proton is moved from the positive plate to the negative plate, what is the magnitude of the change in its electrostatic potential energy?

3 AnswersPhysics3 years ago### Finding a taylor series using binomial series and then adding it to another standard series. So I have the taylor seriers for (1+x)^-3/5?

2/5x+((-3/5)(-8/5))/(2!)x^2+((-3/5)(-8/5)(-13/5))/(3!)x^3+((-3/5)(-8/5)(-13/5)(-18/5))/(4!)x^4

Which I have simplified to

2/5x+(3x8)/(5^2x2!)x^2-(3x8x13)/(5^3x3!)x^3+(3x8x13x18)/(5^4x4!)x^4

and now I need to use this to find the taylor series for (sin x)/(1+x)^-3/5 which I presume is a simple addition job (however im slightly dislexic so am finding it a bit confusing without prior experience)

Can anyone give me a hand adding these two?

Thanks!

1 AnswerMathematics4 years ago### Calculus, greatest and least values on an interval? need quick clarification.?

Morning everyone,

Im working out the greatest and least values on the interval [-3,3]

for the function:

f(x)=2x^3-3x^2-12x+20

Ive got stationary points of -1 and 2

using the standard method ive found the values for f at both stationary points and at both end points of the interval.

My values for f(x)

f(-3)=-16

f(-1)= 28

f(2)= 4

f(3)= 20

From this I can see that my greatest value is when f(-1) and the least is when f(-3).

My question is (ive not studied this before so I appologise if this is a stupid question) but can stationary points be used as the greatest or least values on an interval? I assume so however my text books include no mention and my tutor is not available.

Just need to confirm my assumption (or not)

Thank you!

2 AnswersMathematics5 years ago### First Derivative test help?

Good afternoon,

I need a bit of help.

So ive got my first derivative which is

6x^2-6x-12

(this was the derivative of 2x^3-3x^2-12x+20)

and the stationary points ive found are x=-1 and x=2 at which points the value of the derivative is zero.

So im attempting to classify the points. From my derivative tests

the value of -2 should give a value of 24 which is positive.

6(-2)^2-6(-2)-12 = 24

and a value of 3 should give 24 also which is again positive.

6(3)^2-6(3)-12 = 24

So I would classify my stationary points as a point of inflection? since its positive on both sides of the points?

Is that correct or did I need to simplify the derivative further before applying this test?

And have I gone wrong at any point along the way that you can see?

1 AnswerMathematics5 years ago### Rule of a function?

Hello, ive worked out an inverse function but I cant figure out the rule. Can anyone help?

The function I have is

(9-2x)/(x-5)

So ive done a function table but it doesnt seem to have a rule...

The original function of which this is the inverse was

(1)/(x-2)+5 (x>2)

Can anyone point out where im being a bit silly?

5 AnswersMathematics5 years ago