what is wrong with your work:
you wrote: a = (m3 g - m2 g - m1 g)/m3
but that means m3*a=net force which is NOT true.
NET FORCE= totalmass*acceleration
total mass is Mass1+Mass2+mass3
you cannot apply net force to just one object.
you should have written:
a = (m3 g - m2 g - m1 g)/(m3+m2+m1)
h t t p : / / w w w . j i s k h a . c o m / d i s p l a y . c g i ? i d = 1 2 6 7 3 9 3 5 9 3
ok heres the problem in a picture
h t t p : / / i m g 1 9 2 . i m a g e s h a c k . u s / i m g 1 9 2 / 4 5 0 0 / c a p t u r e x x w . j p g
ok I called the 4 kg block m3 and the 2 kg block m2 and the 1 kg block m1
I don't see what is wrong with my work
a. net force on m3 = m3 a = Fg3 - Fg2 - Fg1
divide by m3 to get a
a = (Fg3 - Fg2 - Fg1)/m3
made it look nice
a = (m3 g - m2 g - m1 g)/m3
= g - (m2g)/m3 - (m1 g)/m3
= g(1 - m2/m3 - m1/m3)
=9.8(1 - 2/4 - 1/4) = 2.5 m/s^2
b. net force on m3 = m3 a = Fg3 - Ft3
solved for the force of tension
Ft3 = -m3(a+g) = -4.0(2.5+9.8)= - 49 N
c. Net force m1 = m1 a = -Fg1 + Ft1
solved for Ft1
Ft1 = m1 (a+g) = 1.0(2.5 + 9.8) = 12 N
2 answers
hmmmmmm thanks