The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

Mechanics help please!!

Hi all,

Can anyone help me with this one?

A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3 N which makes an angle of 30° with the horizontal.
Find the angle that the string makes with the vertical and the tension in the string.

Why is the angle not 60? Surely 90-30 = 60? I have no problems with finding the tension of the string once I have the angle - just so confused on the angle of it! Just need someone to push me in the right direction here :smile: Thank you in advanceeeeee x

Scroll to see replies

Original post by hb763
Hi all,

Can anyone help me with this one?

A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3 N which makes an angle of 30° with the horizontal.
Find the angle that the string makes with the vertical and the tension in the string.

Why is the angle not 60? Surely 90-30 = 60? I have no problems with finding the tension of the string once I have the angle - just so confused on the angle of it! Just need someone to push me in the right direction here :smile: Thank you in advanceeeeee x


Draw a clear diagram and consider the equilibrium of forces via a force triangle.
Reply 2
Avatar for hb763
hb763
OP
5
Resolving:
R(horizontal): 0.3cos30
R(vertical): 0.3sin30 - 5g
Then tried drawing a triangle with this resultant force but unsure what to do with it?
Draw a clear diagram and consider the equilibrium of forces via a force triangle.
Original post by hb763
Resolving:
R(horizontal): 0.3cos30
R(vertical): 0.3sin30 - 5g
Then tried drawing a triangle with this resultant force but unsure what to do with it?

No don't resolve, just draw a force triangle.

So draw a free body diagram of the 3 forces acting on the mass. And put these forces tip to toe forming a closed triangle.
Then you can find the angle and tension using trigonometry etc.

You can do it by resolving too but it's better to do it this way.
There is no resultant force acting on the mass, it's in equilibrium hence the closed force polygon.
Reply 4
Avatar for hb763
hb763
OP
5
I have never drawn a force triangle in my life to be honest, have always been taught to resolve in both directions.
Original post by Anonymouspsych
No don't resolve, just draw a force triangle.

So draw a free body diagram of the 3 forces acting on the mass. And put these forces tip to toe forming a closed triangle.
Then you can find the angle and tension using trigonometry etc.

You can do it by resolving too but it's better to do it this way.
There is no resultant force acting on the mass, it's in equilibrium hence the closed force polygon.
Original post by hb763
I have never drawn a force triangle in my life to be honest, have always been taught to resolve in both directions.

Well in that case you're going to have to solve two simultaneous equations coming from horizontal and vertical equilibrium. You can't find the angle on its own and then find the tension which seems like what you're trying to do. Let θ = angle tension makes with vertical and T=tension in string:

Horizontally: 0.3cos(30) = T sinθ

Vertically: Tcosθ +0.3sin(30) = mg

You can solve the above equations simultaneously and find what θ and T are
Reply 6
Avatar for hb763
hb763
OP
5
Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?
exactly
Original post by hb763
Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?
Reply 8
Avatar for ck4203
ck4203
3
What's the answers?
Reply 9
Avatar for ck4203
ck4203
3
Original post by hb763
Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?


Do you still have the answers to these?
For all you lazy ****s out there, the answers are:

37.4°
and 0.428N

: )
You're welcome for helping with the Integral test.
Original post by TheoP31
For all you lazy ****s out there, the answers are:

37.4°
and 0.428N

: )
You're welcome for helping with the Integral test.

you fancy helping out with the other ones too??:colondollar:
Original post by d r e a m y
you fancy helping out with the other ones too??:colondollar:

By the word “help” you mean you want the answers lol, or do you want screenshots of the solutions?
Original post by TheoP31
By the word “help” you mean you want the answers lol, or do you want screenshots of the solutions?

solutions pleasee but only for 3,4,5 cause i understood all the others
Original post by TheoP31
By the word “help” you mean you want the answers lol, or do you want screenshots of the solutions?

MY GUYYY;((( where'd u go
absolute lifesaver TYSMMMM
Original post by TheoP31
Chillax, I'm here!! :smile:
I have attached the solutions below, hope they help!

Q3.jpg

Q4.jpg

Q5.jpg

Do you recommend any channels/vids for this topic?
Original post by d r e a m y
Do you recommend any channels/vids for this topic?

TL Maths is a good YouTube channel!
Original post by laurawatt
TL Maths is a good YouTube channel!

Thank you:smile: Also, do you know any channels with content specific for WJEC?
Original post by d r e a m y
Thank you:smile: Also, do you know any channels with content specific for WJEC?

A lot of the content is the exact same anyway. TLMaths is one of the good channels tbh, like Laura said!

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you