I'm a little bit confused by one of the questions. It is scoring marks for something which it doesn't appear to be asking for.
It's AQA Unit 5 June 2011 Question 2b.
"For the reaction to take place the a particle must come within a distance, d, from
the centre of the aluminium nucleus.
Calculate d if the nuclear reaction occurs when the a particle is given an initial
kinetic energy of at least 2.18 × 10–12 J."
The question then suggests that I use (Q1.Q2)/(4.pi.Eo.r) as the energy.
So I rearrange the equation to move the provided kinetic energy to the bottom of the equation, and bring the radius up as the subject in order to calculate it. I get the correct answer, which is about 2.75e-15 metres.
However, calculating that is just worth 2 of the 3 points. There is a further point in the mark scheme for writing:
"kinetic energy lost by the α particle approaching the nucleus is equal to the potential energy gain"
I'm really lost as to why they want me to state that. Do I lose the mark for not writing that? I achieved all the other marks for that question. I have the mark for using the correct equation in the right way. Does that provide a mathemetical equivalent to writing down the worded answer?
i dont think so, i was actually doing this question like 3 hours ago funnily enough!
basically as long as you show that potential=kinetic in your workings directly or indirectly you get the mark, you wouldnt have to put it in words and all that