Diving Board Question

[TheHamburgler1]

Im not sure if I have to add both weights and if so I don't know if I am adding them to the right spots.

Q) A 596N diver is standing at the edge of a diving board, 1.9m from the fulcrum of a 114N diving board. The fulcrum is located 2.1m from where it is bolted at the opposite end

Find the force the fulcrum exerts on the diving board.

My only question is whether or not I add both 596 and 114 to get 710 and then use 710 or do I only use 596?

so far I have: -F1+F2+-w1+-w2 should I add -w2 or not?

 

[physics girl phd]

What are your variables (F1, F2, w1, w2)? and what is your thinking behind your equations?

And what do you mean by "use 710" or "use 596"? for what? is there a part b (maybe something involving torque?), or are you just looking for the force exerted by the fulcrum?

Try to clarify your thoughts for us.

 

[TheHamburgler1]

I'm only looking for the force that the fulcrum exerts and I thought I had to use the torque equation in order to find it with what I am given, or am I mistaken? by 710 I meant the combined weight of the person and the board.

 

[physics girl phd]

That answer would then be right... you don't need to think about using the torque equation unless you had an additional unknown force (two unknowns would need two equations... one for the net force and one for the net torque). You might want to look at this developing thread for a problem like that (see how yours is simple in comparison?):
https://www.physicsforums.com/showthread.php?t=143612

PS -- ALWAYS use units (710N)

 

[TheHamburgler1]

Im sorry, I do not know either F2 or F1 therefore I can't use that equation can I?

 

[physics girl phd]

You still haven't said what you've defined as F1, F2, w1, w2, etc... or what equation you are particularly using. If you are thinking of using torque, torque is related to force times distance. if you are using forces, then what forces pushing down would equal what forces pushing up, so that net force was zero?

I think you might want to read about this somewhere in your text again. You seem :uhh: confused.

 

[TheHamburgler1]

F1 is the bolt force F2 is the fulcrumforce W1 is the person weight W2 is the board weight

 

[physics girl phd]

This is the first time you've mentioned a "bolt" where is that?

I propose you do the following.

1) draw a free body diagram of the system.
2) if you are at equilibrium, the net force and net torque are zero. Using these you should be able to determine all the unknowns.

 

[TheHamburgler1]

and this leads back to my main question of whether or not when using W to find F2 if I add the person and the board together to get 710 or do I do something different witht the two weights

 

[physics girl phd]

And this leads me back to saying -- can you then attach a free body diagram of the system -- showing where you are getting a net force or torque?

 

[TheHamburgler1]

I just got the answer thanks

 

[physics girl phd]

I always first -- draw a free body diagram.
second -- write an net force equation: forces up = forces down.
third -- write a net torque equation: torques making it pivot left = torques making it pivot right.
fourth -- solve the equations.

This is what YOU have to do.

 

[TheHamburgler1]

I got the answer to be 1352.38N

 

[physics girl phd]

Show your work?

 

[TheHamburgler1]

F2r+-wr=F2(2.1)+-710(4)=280/2.1=1352.38

 

[TheHamburgler1]

Right? Wrong?