text: # Homework Help: A question on work, power and energy
  
  1. May 1, 2014
  
  ### ritik.dutta3
  
  1. The problem statement, all variables and given/known data
  The two blocks in an Atwood machine have masses 2 kg and 3 kg. Find the work done by gravity during the fourth second after the system is released from rest.
  
  2. Relevant equations
  Work done by gravity= mgh
  
  3. The attempt at a solution
  Both the masses will have the same acceleration 'a'. Let T be the tension in the string.
  m1= 2 kg, m2= 3 kg, g= 10 m/s^2
  
  T-m1g=m1a
  therefore, T- 20= 2a
  
  m2g- T= m2a
  therefore, 30 - T= 3a
  on solving both the equations, a= 2 m/s^2
  
  distance travelled by the blocks would be 1/2(at^2). So, the heavier block would travel 16 m downwards and the lighter block 16 m upwards.
  Net mass= 3-2= 1 kg
  hence, the work done should be
  W= mgh= 1 x 10 x 16 = 160J
  
  where am I going wrong?
  1. The problem statement, all variables and given/known data
  
  2. Relevant equations
  
  3. The attempt at a solution
  
  2. May 1, 2014
  
  ### Tanya Sharma
  
  You have used distance traveled in 4 seconds .Whereas you need distance traveled during the 4th second i.e between 3rd and 4th sec.
  
  3. May 1, 2014
  
  ### ritik.dutta3
  
  Got it! Thanks! :D