 #1
 30
 5
Homework Statement
Homework Equations
F = m*a
The Attempt at a Solution
[/B]
Hello, i think i understand d and e so only the first three tasks are important.
a) a = (m2  m1)/(m1 + m2) *g > (5kg  2kg)/(2kg+5kg) *10ms^2 = 4.29 ms^2
T = m1 (a+g) > 2kg (4.29ms^2 + 10ms^2) = 28 N
So i know the answer is 20N but im not sure why i got it wrong. Is it because block B stands on the ground and because of that the acceleration is 0?
b) The upward force should be the same magnitude as the downward force on block B.
Downward force = weight = 5kg * 10ms^2 = 50N
Upward force = only normal force? = 50N
My problem here lies in my mistake from a i think. So does block B has tension force on it? Im kinda confused because block B rests on ground, so does it even have tension then? I mean if the acceleration from block A is really 0, then shouldnt the tension be zero as well?
c) total downward force of the pulley = weight from block A and B + weight of the pulley
20N + 50N + 15N = 85N
These should be the only forces acting downwards on the system but apparently this is wrong too. It should be 55N but i´m not sure why it should be this value. The tension force should be pointing upwards and the weight downwards, even if i subtract the tension force i wont get 55N.
Sorry for so much text. I hope someone can clarify this to me. Thanks for every answer.
Attachments

218.6 KB Views: 712