Forces, Newton's laws and moments

• Inextensible string mean

  Acceleration of both particles is the same
• Light string mean

  The string has no mass and tension is the same
• Pulley is smooth mean

  No friction so tension in the string is the same on both sides
• Pulley is fixed

  Cannot move although forces can still act upon it
• Equation for tension for the smallest mass(pulleys)

  T - mg = ma
• Equation for tension for the largest mass (pulleys)

  mg - T = ma