Sarahisme Posted March 31, 2005 Share Posted March 31, 2005 hey again...got another physics question i need some help with (or help making sure i am actually getting the right answer)..... The light isotope of lithium, 5Li, is unstable and breaks up into a proton (hydrogen nucleus) and an α particle (helium nucleus). In this process, a total of 3.15 x 10-13 J is released, appearing as the kinetic energy of the two reaction products. Determine the velocities of the proton and α particle that arise from the decay of a 5Li nucleus at rest. ( Note: The masses of the proton and alpha particle are mp = 1.56 x 10-27 kg and mα = 4mp = 6.68 x 10-27 kg.) i am working on it now, but i thought i'd give peoples the heads up first... i will post my attempt at a solution in a bit... Cheers Sarah Link to comment Share on other sites More sharing options...
Sarahisme Posted March 31, 2005 Author Share Posted March 31, 2005 lol its a lot of working so i won't write it all out here just yet.... but the gerneral gist i think is that you use initial momentum = final momentum ie. m1v1 = m2v2 and that KEf = PEi ie. .5*m1*v1^2 + .5*m1*v2^2 = 3.15 x 10-13 J and using the second equation there you get the v2 in terms of v1, then sub it into the first equation (momentum one) and get a numerical answer for v1. It is then easy to also compute v2. so after doing this i get. Velocity of proton (hydrogen nucleus) = 2.32 x 10^7 m/s and Velocity of alpha particle = -5.80 x 10^6 m/s Sarah... Link to comment Share on other sites More sharing options...
Sarahisme Posted March 31, 2005 Author Share Posted March 31, 2005 only thing is i used mass of alpha particle = 4 x proton mass but i dunno in the question it says that mp = 1.56 x 10-27 kg and mα = 4mp = 6.68 x 10-27 kg but 4 x 1.56 = 6.24 !!!! not 6.68??? well anywho...what do you guys think? Link to comment Share on other sites More sharing options...
Sarahisme Posted March 31, 2005 Author Share Posted March 31, 2005 actually i redid it because i mistyped the question and the protons mass should be 1.67 x 10^-27 kg so i now get Velocity of Proton = 7.94 x 10^-7 m/s and Velocity of Alpha Particle = -1.98 x 10^-7 m/s sorry if i didnt show complete working but i am in a really really big rush so can someone tell me if this is right? cheers and thanks Sarah :) Link to comment Share on other sites More sharing options...
Sarahisme Posted March 31, 2005 Author Share Posted March 31, 2005 lol sorry sorry!!! after a good night sleeping on it....i have changed my answers and this time i know i'm right (...well i hope so anyways ) I get Velocity of proton (hydrogen nucleus) = 1.74 x 10^7 m/s and Velocity of alpha particle = -4.34 x 10^6 m/s Link to comment Share on other sites More sharing options...
Sarahisme Posted March 31, 2005 Author Share Posted March 31, 2005 lol just thought i'd make it clear hehe Link to comment Share on other sites More sharing options...
Dapthar Posted March 31, 2005 Share Posted March 31, 2005 so can someone tell me if this is right?I ended up getting [math]v_p\approx1.737228848 \cdot 10^7[/math][math]m/s[/math] [math]v_\alpha\approx-4.34307212 \cdot 10^6[/math][math]m/s[/math]. Where [math]v_p[/math] is the velocity of the proton, and [math]v_\alpha[/math] is the velocity of the alpha particle. Of course, [math]v_p\approx-1.737228848 \cdot 10^7[/math][math]m/s[/math] [math]v_\alpha\approx4.34307212 \cdot 10^6[/math][math]m/s[/math] is correct as well. Link to comment Share on other sites More sharing options...
Sarahisme Posted April 1, 2005 Author Share Posted April 1, 2005 lol cool thanks Dap thats what i ended up getting too lol after a long time ! Link to comment Share on other sites More sharing options...
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