Engineering maths problem

• mFBk

  30 Jul 09, 19:19

  Hi... i need some help on engineering maths problem.. Hope someone can help me to find a solution to it... Tried to solve but cant...

  Here is the question :

  A certain radioactive material is known to decay at a rate proportional to the amount present. There are 200mg of the material present initially. After 5 hours, it is observed the material has lost 10% of the original mass. Let m denote the mass of the material remaining at the time, t.

   

  (a) Write down the differential equation which describes the rate of change of m with respect to t?

   

  (b) Solve the differential equation.

   

  (c) Find the mass of the material present after 10hours.

   

  (d) How long will it take for the material to decay to half its original mass?

• deepak.c

  30 Jul 09, 19:25

   

  I hope this helps, it's similar.

   

  http://www.sgforums.com/forums/2297/topics/362727

   

• Deadstroke

  31 Jul 09, 01:30

  I am assuming you know your stuff, so skip some steps.

   

  1. dM/dt = kt

  2. Solve the above, M = Aexp(kt), A and k are constants

  3. plug in inital and t=5 values to solve for A and k