translational Equilibrium and downward force

[cholton]

New to forum. Learning Phys I on my own distant learning. I get Trans. Equil as sum of all forces = 0 however choices not so simple. Choices are:

1) only if at rest

2) only if moving at constant velocity

3) only if it is either at rest or moving with constant velocity

4) if it is moving with either constant velocity or constant acceleration

 

 

boy (unk mass)-----4m--------(fulcrum)----1m-----80kg man

balanced

 

What is downward force exerted on fulcrum?

1) zero Newtons

2) 100N

3) 600N

4) 800N

5) 1000N

[timo]

For the 1st questions you just have to look at F=m*a or equivalently a = F/m, where a is the acceleration (the change in velocity), m the mass of the object and F the total force acting on it (which is zero by your conditions).

 

In case of the 2nd question, you´ll first have to figure out the boy's mass by using the conditions for the system to be balanced.

[cholton]

Alright...stupid? I am!

 

Read it like 10 times and it got worse! Don't understand what you were telling me! I am really LOST! ! could someone break it donw for my like really well. the medicine I am on is making me wonder about my own name it seems. No really!! thanks much!

[swansont]

The first question is poorly done (technically two correct answers) but if you're lost on this, discuss the validity of each answer, and we can give you feedback.

 

For the second, as Atheist said, you need to solve for the equilibrium condition of the balance. But you can eliminate several choices even before you do that.