Need help on some mechanics questions from a text book

AI Thread Summary
The discussion revolves around a user struggling with basic mechanics questions from a textbook, particularly focusing on the support force from a slope and the correct representation of forces on an object. Participants emphasize the importance of clear diagrams and accurate calculations, pointing out that the user had included incorrect forces and rounded intermediate results improperly. They encourage the user to avoid unnecessary complexity in problem-solving and provide guidance on using trigonometric functions correctly. The user expresses gratitude for the assistance, acknowledging that their initial approach was overly complicated. Overall, the conversation highlights the need for clarity and precision in understanding physics problems.
TheePhysicsStudent
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Homework Statement
I know HOW to get the answer as i underwent trial and error, but I don't actually understand the process of why we do what we do:
Relevant Equations
Friction = mgsin θ
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These are the questions I am failing to comprehend despite their very basic nature
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This is the wonderful support from the book explaining how to get the answer ! (It just gives you the answer no working out which is annoying)
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I
 
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I would like to start with 2 B II, the support force from the slope on the object
 
TheePhysicsStudent said:
I would like to start with 2 B II, the support force from the slope on the object
Sorry i looked at the wrong question, I meant Question 4 sorry for any inconvenience I caused you
 
TheePhysicsStudent said:
Sorry i looked at the wrong question, I meant Question 4 sorry for any inconvenience I caused you
No need to apologize: we help voluntarily :smile:

In the mean time I have looked at the first one (2a) and I do have comments on that one:

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You are asked to show the three forces on the object. I see four arrows; two are correct and one is missing

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Agree ?

You are also asked for the support force from the slope acting on the object. Any suggestions ?

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Re Question 4 (PF prefers one item per thread to facilitate referencing and avoid confusion, but never mind...)

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What you appear to do looks OK to me, but you are just like the book: you don't tell. What's the very basic nature under this one ?

Equilibrium ##\Leftrightarrow## sum of forces is zero

A better drawing is in order: in your picture the tensions don't act on the object

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And somehow I get 6.96, i.e. 7.0 N, not 6.8

(golden rule: don't round off intermediate results).

The picture I had in mind:

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General idea clear now ? Basic nature :wink: ?
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BvU said:
(golden rule: don't round off intermediate results).
Platinum rule: Don't find intermediate angles if you are looking for trig functions.

FBD_Hanging_mass.png

Here, $$\sin\theta=\frac{0.80}{\sqrt{0.12^2+0.80^2}}~;~~\cos\theta=\frac{0.12}{\sqrt{0.12^2+0.80^2}}~;~~\tan\theta=\frac{0.80}{0.12}.$$ :wink:
 
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Ancient dutch expression: there's always boss above boss

Ancient greek expression: turtles all the way down

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WOW! I can't thank you enough, especially for question 4 as I realise that whilst I was sort of there I made it so much weirder than it had to be, Many thanks to you guys
 
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