Mechanics questions from textbook

[TheePhysicsStudent]

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

These are the questions I am failing to comprehend despite their very basic nature

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)

I

 

[BvU]

Hello @TheePhysicsStudent ,

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And which one do you want to start with ?

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

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[TheePhysicsStudent]

I would like to start with 2 B II, the support force from the slope on the object

 

[TheePhysicsStudent]

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

 

[BvU]

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

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

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

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...)

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 ?

Spoiler

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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[BvU]

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:

General idea clear now ? Basic nature ?

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[kuruman]

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

Platinum rule: Don't find intermediate angles if you are looking for trig functions.

Here, $$\sin\theta=\frac{0.80}{\sqrt{0.12^2+0.80^2}}~;~~\cos\theta=\frac{0.12}{\sqrt{0.12^2+0.80^2}}~;~~\tan\theta=\frac{0.80}{0.12}.$$

 

[BvU]

Ancient dutch expression: there's always boss above boss

Ancient greek expression: turtles all the way down

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[TheePhysicsStudent]

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