An Atwood's machine is built from m1=1kg and m2=2kg. The mass less string is passed over a friction less, mass less pulley. When the system is released from rest, what is the tension in the string?

Answer 1

force down:2*9.8
force up: 1*9.8
Net force= forcedown-forceup=ma

solve for a: mass=3kg
(9.8)(2-1)=3*a
a= 9.8/3
tension= mass*g-+mass*acceleration
tensionheavy side= 2(g-g/3)=4g/3
tensionlight side=1g+1g/3=4g/3