Forces of a wrecking ball against a wall at rest.

AI Thread Summary
A user seeks help with a physics problem involving a 200kg wrecking ball resting against a wall, suspended by a cable at a 9° angle. They struggle with applying Newton's second law and drawing a correct free body diagram, initially mislabeling forces. Respondents clarify that weight acts vertically, and reaction forces on a frictionless surface are normal, emphasizing the simplicity of mechanics. The discussion highlights the importance of correctly identifying forces without overcomplicating the analysis. Understanding these fundamental concepts is crucial for solving the problem effectively.
physicalConst
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Hello everyone, this is my first time posting to these forums, and my first time posting any online help regarding math. As you can imagine, this is a bit awkward and embarrassing for me. My textbook has no examples of the type of problem below and hours of googling has failed me. Hopefully someone would be kind enough to help me with my dilemma!

Question Description
A wrecking ball that has a mass of 200kg is resting against a wall. It hangs from a cable from the top of a crane that is touching the wall. The cable makes an angle of 9° with the wall. Ignore friction between the wall and ball.

Questions To Be Answered
  1. Apply Newtons second law, but do not substitute the letters for numbers.
  2. What is the magnitude and direction of the force of the wrecking ball on the wall?

As always I attempted to draw a free body diagram but became instantly stuck. From the picture I attached, you can see the two FBD I drew. In the first one I encountered a force which I could not label. I felt like it should be classified as weight, but that would give me two weight forces in differing directions.

http://db.tt/v3KiVQvS
 
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welcome to pf!

hello physicalConst! welcome to pf! :smile:

your top diagram (with four arrows), i don't understand at all :confused:

your bottom diagram is correct (with only 3 forces), except of course that weight is always vertical :wink:
 
Thanks for your response tiny-tim!

When I made the first diagram I was also confused, I couldn't see how it could be possibly right, but I though I missing something about the fundamentals of forces. So I drew up that second diagram, and although I knew that weight should be vertical, the whole pushing against the wall threw me. I think I over analyzed the whole problem.
 
hi physicalConst! :smile:

(just got up :zzz:)
physicalConst said:
I think I over analyzed the whole problem.

yeah! :biggrin:

don't do that … mechanics really is usually quite simple!

weight is always vertical, reaction forces on a frictionless surface are always normal, and tension is always along the cable or string :wink:

(and if you can't think of a reason for a force … it isn't there!)​
 

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