khimberleigh Posted March 9, 2013 Report Share Posted March 9, 2013 Please help me with this question, I've been stuck for ages. 'Imagine an astronaut 2m outside the exterior walls of the Space shuttle, and 10m from the centre of mass of the Space shuttle. By making appropriate assumptions and approximations, calculate how long it would take for this astronaut to be pulled back to the Space shuttle by the force of gravity alone.'The mass of the Space Shuttle is: 6.8 x 10^4 kgThanks in advance Reply Link to post Share on other sites More sharing options...
paki95 Posted March 18, 2013 Report Share Posted March 18, 2013 Physics Forces LabForces Lab.docx Reply Link to post Share on other sites More sharing options...
macrofire Posted April 3, 2013 Report Share Posted April 3, 2013 Please help me with this question, I've been stuck for ages.'Imagine an astronaut 2m outside the exterior walls of the Space shuttle, and 10m from the centre of mass of the Space shuttle. By making appropriate assumptions and approximations, calculate how long it would take for this astronaut to be pulled back to the Space shuttle by the force of gravity alone.'The mass of the Space Shuttle is: 6.8 x 10^4 kgThanks in advancehttp://physics.stackexchange.com/questions/19813/calculating-gravity-when-taking-into-account-the-change-of-gravitational-forceI thought about it for a while, and then I found this. Take a look at some of the stuff and their links to other works on the same topic. If it doesn't make sense, tell me. On another note, can anyone explain the Lie Group SU(3) and how that relates to Quantum Chromodynamics? If you could give a simple analogy, that would be great. Reply Link to post Share on other sites More sharing options...
googly Posted April 17, 2013 Report Share Posted April 17, 2013 WHICH ARE THE EASIEST OPTIONS FOR PHYSICS HL PAPER3?please help cuz my exams in a week! Reply Link to post Share on other sites More sharing options...
ChocolateDrop Posted April 17, 2013 Report Share Posted April 17, 2013 (edited) WHICH ARE THE EASIEST OPTIONS FOR PHYSICS HL PAPER3?please help cuz my exams in a week!Option G Electromagnetic waves is easy to grasp, and if you do not mind memorisation and space I hear Astrophysics is alright. Edited April 17, 2013 by ChocolateDrop Reply Link to post Share on other sites More sharing options...
MLI Posted April 18, 2013 Report Share Posted April 18, 2013 WHICH ARE THE EASIEST OPTIONS FOR PHYSICS HL PAPER3?please help cuz my exams in a week!I am not really good at physics, I chose astrophysics and medical physics and i found them okay , they are not that hard. Reply Link to post Share on other sites More sharing options...
The Rainbow Connection Posted August 18, 2013 Report Share Posted August 18, 2013 Question: I don't understand why D is the answer - anyone help please A cell of emf ε and internal resistance r delivers current to a small electric motor.motor. 450 C of charge flows through the motor and 9000 J of energy are converted in the motor. 1800 J are dissipated in the cell. The emf of the cell is A. 4.0V. B. 16V. C. 20V. D. 24V. Reply Link to post Share on other sites More sharing options...
The Rainbow Connection Posted August 19, 2013 Report Share Posted August 19, 2013 V = 10,800 J / 450 C = 24 V.This means that the emf is 24 V, which corresponds to D.Wow that was really clear and helpful! thank you very much Reply Link to post Share on other sites More sharing options...
Dave Ev Posted September 25, 2013 Report Share Posted September 25, 2013 <p>You walk up a 1000m high mountain, which takes you 5 hours. Walking on the flat consumes about 400W. You are hoping to lose some of your 70kg mass with all this exercise but on the way you eat 4 small chocolate bars, which according to the wrapper will each supply 1130KJA) Calculate the energy you expend during the 5 hour walk. While you're climbing your body only works at a 15% efficiency.I got 48 MJ as the totalB) Calculate the energy that must be obtained from your body after the energy of the chocolate has been used.I got 4520KJ (but i'm not sure whether to account for the efficiency)C) If fat converts to energy at a rate of 38MJkg-1, how much mass are you likely to lose?This answer seems the worst so I'll refrain from saying http://www.ibsurvival.com/public/style_emoticons/#EMO_DIR#/tongue.png400W, 15%=60W5*60*60=18000A watt is J/s so in 5 hours you would use 60J*18000s=1,080,000J or 1.08MJSo for the walk you need 1.08MJ, the bars will provide 4*1130KJ which is 4520KJ (4.52MJ) but you will only use 15% of that so the bars provided an actualy energy output of 0.678MJ which means your body will provide 1.08-0.678=0.402MJ(If you didn't account for efficient in this part you would have gotten a negative number http://www.ibsurvival.com/public/style_emoticons/#EMO_DIR#/pinch.gif)0.402/38=0.0106Kg.Surely, mgh states 70*9.81*1000 is the energy needed to get to the top.of the hill. At 15% efficiency that would mean required energy isPerson Energy = 70*9.81*1000/15%The residual after chocolate is Residual Energy = 4*1130,000 - Person EnergyThen take Residual and figure our how many kg are lost due to the Residual being negative, as in the chocolate was less than that used up the hill.Not sure why I need to know flat walking value 400W.. Reply Link to post Share on other sites More sharing options...
Dwight K Shrute Posted October 27, 2013 Report Share Posted October 27, 2013 Hi guys I need some help with an uncertainty question.If I wanted to calculate the weight of an object, I would use F=mg. I know 'g' and the mass is written on the object (let's say 100g). So F=(0.1)(9.81). But what are the uncertainties in this? Since the mass is written on the object, I did not have to weigh it on a weighing machine so I don't really see a source of uncertainty. So is the uncertainty 0 or should I just estimate an uncertainty? Reply Link to post Share on other sites More sharing options...
maroctam Posted October 27, 2013 Report Share Posted October 27, 2013 Hi guys I need some help with an uncertainty question.If I wanted to calculate the weight of an object, I would use F=mg. I know 'g' and the mass is written on the object (let's say 100g). So F=(0.1)(9.81). But what are the uncertainties in this? Since the mass is written on the object, I did not have to weigh it on a weighing machine so I don't really see a source of uncertainty. So is the uncertainty 0 or should I just estimate an uncertainty? Is this for a lab? Assuming it is, and that mass is your IV then yeah, uncertainty would be zero and you can explain that by saying it's a standard mass or something of the sort - that's what our teacher told us to do. Reply Link to post Share on other sites More sharing options...
AnnaBananaBread Posted February 7, 2014 Report Share Posted February 7, 2014 Hi guys! Could anyone please explain electricity and magnetism in a nutshell to me, please? I realise that this is a very very broad topic, but any help at all would be so appreciated, particularly with the formulas involved, right-hand rule, and magnetic flux...Sorry if someone has already asked any of this also! Reply Link to post Share on other sites More sharing options...
Emmi Posted February 7, 2014 Report Share Posted February 7, 2014 Hi guys! Could anyone please explain electricity and magnetism in a nutshell to me, please? I realise that this is a very very broad topic, but any help at all would be so appreciated, particularly with the formulas involved, right-hand rule, and magnetic flux...Sorry if someone has already asked any of this also!This is such a broad topic that no one can really give a short summary on because there's so much, what in particular do you have questions about? Reply Link to post Share on other sites More sharing options...
AnnaBananaBread Posted February 8, 2014 Report Share Posted February 8, 2014 Hi guys! Could anyone please explain electricity and magnetism in a nutshell to me, please? I realise that this is a very very broad topic, but any help at all would be so appreciated, particularly with the formulas involved, right-hand rule, and magnetic flux...Sorry if someone has already asked any of this also!This is such a broad topic that no one can really give a short summary on because there's so much, what in particular do you have questions about?Yeah...Sorry about that, I should've been more specific! I just generally had a really tough time with electricity and magnetism as it was the first thing we learned for Physics HL, so if anyone knows any really great places to review/understand the concepts and any study guides that would be lovely! For particular questions I would say maybe how to find EMF and how it affects other variables, and the force exerted by current carrying wires. Those two I found particularly difficult!Thank you so much and also I appreciate the "R U Mine", haha Reply Link to post Share on other sites More sharing options...
khimberleigh Posted February 8, 2014 Report Share Posted February 8, 2014 Emf is the power supplied by the supply per unit current. That's the definition IB wants you to know. Although the underlined bit sounds redundant, in one of the past papers I did you actually had to state that in order to get any marks.There are two main ways of finding emf. They are both in the data booklet. The first one is e=BLvWhere B is magnetic field strengthL is length on conductorv is velocity of the conductorThe syllabus says that you need to be able to derive that one. Deriving questions rarely come up but you should probably know it just in case.To understand the derivation you need to first know how emf is induced. Conductors (eg a piece of wire) contain free electrons. When a conductor moves through a magnetic field, the electrons experience a force. This force causes the electrons to move to one side of the conductor, and the atoms on the other side become positively charged. Now the conductor has a positive and a negative side which creates a potential difference (voltage) between the two sides. The electrons will stay where they are because the magnetic force and the electric force are at equilibrium.So the derivation is:F(B)=F(E)qvB=EqE=vB(delta)V=EL (delta)V=vBLe=vBLq is charge, v is velocity, B is magnetic field strength, E is electric field strength, L is length, (delta)V is change in voltage and e is emf.The other formula is based of Faraday's Law which says that 'An induced emf is proportional to the rate of change of the flux linkage'e= -N(change in flux linkage / change in time) where N is the number of turns of wire.I hope that kind of helps. Which other variables to you mean that are affected by emf? Reply Link to post Share on other sites More sharing options...
Stefan Posted March 2, 2014 Report Share Posted March 2, 2014 (edited) Hi guys,i need help on a question regarding thermal physics!An ideal gas expands isothermally from a state X to a new state of volume V. The work done by the gas is W. Which of the following is correct for an adiabatic expansion of the gas from state X to a new state of volume V? Change in internal energy - work doneA. Delta U>0 - greater than WB. Delta U<0 - greater than WC. Delta U>0 - less than WD. Delta U<0 - less than W Edited March 2, 2014 by Stefan Reply Link to post Share on other sites More sharing options...
Osshe Louis Posted May 5, 2014 Report Share Posted May 5, 2014 My exams is in 2 days timeand im not even confident about paper 1 and paper 2 and i took physics HLmy school didnt have the proper teacher for nearly 1 semester which forced most of us to study by ourselfis there any suggestion of web/links that might help me?for the few of mock exam conducted by my tuition course,i always get a pretty bad marksThanks! Reply Link to post Share on other sites More sharing options...
XeoKnight Posted May 7, 2014 Report Share Posted May 7, 2014 In case anyone sees this, quick q!For the Physics option, Astrophysics, do we have to be able to calculate the critical mass for the 'big crunch' of the universe? Reply Link to post Share on other sites More sharing options...
SYL Posted March 27, 2015 Report Share Posted March 27, 2015 (edited) Hi guys,i need help on a question regarding thermal physics!An ideal gas expands isothermally from a state X to a new state of volume V. The work done by the gas is W. Which of the following is correct for an adiabatic expansion of the gas from state X to a new state of volume V? Change in internal energy - work doneA. Delta U>0 - greater than WB. Delta U<0 - greater than WC. Delta U>0 - less than WD. Delta U<0 - less than WSince transfer of thermal energy = change in internal enetgy + work done by system, i.e Q= U +W . In an Adiabatic expansion Q=0( see definition), so U =-W whcih is negative so <0, and Work done un an adiabatic expansion will be less as it is the area underneath the curve, which curves below the isothermal one Edited March 27, 2015 by SYL Reply Link to post Share on other sites More sharing options...
Cici2017 Posted July 18, 2017 Report Share Posted July 18, 2017 Help! Reply Link to post Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.