9921126a   
   From: postings@REMOVE-TO-REPLYconfidential-counselling.com   
      
   In article   
   ,   
    dotcom  wrote:   
      
   > I thought I understood  basic gravity problems but the following high   
   > school physics problem from my daughter has me stumped ( I think)   
   > Q. a disabled ( meaning of disable not defined) satellite of mass   
   > 2400kg  is in orbit at a ht of 2000 km above the earth  at a speed of   
   > 6900 m/s. ( my calc show that is exaclty the speed required for a   
   > circular orbit at that ht).  it then says the satelite falls to a ht   
   > of 800 km calculate  what the new speed at the lower ht..   
   > well I simply calculated the gain in potential energy ( PE =  delta   
   > GMm/r)  and equated this to the gain in kinetic energy ( =0.5 mv^2)   
   > as the satellite must speed up. and added this to the original speed   
   > of 6900 m/s to get 10870 m/s , but I am not sure that this correct.   
   > it certainly doesnt give me the answer in the school text book of 7900   
   > m/s   
   >   
   > ( I used G=6.67E-11, M =5.98E24 kg and r= 6.38E6 m.   
   > using this the loss in potential energy = 1.9E10 J   
   >   
   > I suspect I am going wrong somewhere in not accounting for the fact   
   > velocity is a vector quantitiy. Surely it must depend on the direction   
   > the satellite is heading initally. is this really a solvable problem?   
      
   Sadly I dont have the maths to work this out, but since this is only   
   high school work, perhaps you just need to calculate the speed at 800km   
      
   You guys are very cluey, but you wouldn't expect a school student to do   
   all other stuff you are considering   
      
      
      
   Perhaps someone could just calculate the speed required to keep it in   
   orbit at 800km   
      
   David who is trying to learn maths, but...   
      
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