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Help - confused with this physics question PLEASE

Ill attach the image below - but since we're given the weight of the particle and the angle to the normal would the vertical weight downwards be Wcos4??? Ans then you can use triangle of forces to determine the electric force to the left?

But the Markscheme ignores this multiplication of cos4 and just wrote (1.7*10^-2)*tan4

Why is this??? Am i visualising it wrong..
Reply 2
Tcos4 is equal to the weight where T is the tension in the thread
The vertical component of the tension is W, and the horizontal component is the electrical force, i.e. adjacent and opposite to the angle, hence tan.
Reply 4
Original post by RogerOxon
The vertical component of the tension is W, and the horizontal component is the electrical force, i.e. adjacent and opposite to the angle, hence tan.


Ohh - so they've basically given me the vertical component by giving me the weight?
Original post by MrToodles4
Ohh - so they've basically given me the vertical component by giving me the weight?

Yes. For equilibrium vertically, the weight must equal the vertical component of the tension.
Reply 6
1.7x10^-2 is the vertical component. so it's tension is: Tcos4=1.7x10^-3, rearrange to find in terms of T, which will be T=(1.7x10^-2)/(cos4). now to find the vertical component it's simply ANSsin4=1.1887...x10^-2 which is approximately 1.2x10^-3 newtons. I find doing this much simpler than using tan as I am able to visualize what I'm doing at every step much easier than I am with tan, hope this helps.
(edited 5 years ago)
Reply 7
Original post by Jono*
1.7x10^-2 is the vertical component. so it's tension is: Tcos4=1.2x10^-3, rearrange to find in terms of T, which will be T=(1.2x10^-2)/(cos4). now to find the vertical component it's simply ANSsin4=1.1887...x10^-2 which is approximately 1.2x10^-3 newtons. I find doing this much simpler than using tan as I am able to visualize what I'm doing at every step much easier than I am with tan, hope this helps.


Thanks for the reply, If 1.7*10^-2 is the vertical component wouldn't Tcos4 = 1.7*10^-2?
Reply 8
Original post by MrToodles4
Thanks for the reply, If 1.7*10^-2 is the vertical component wouldn't Tcos4 = 1.7*10^-2?


Yes, that was a mistake on my part when typing it out.

I've edited it to show the correct values now
(edited 5 years ago)

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