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m2 help

Need help with q2.

https://9565af48d144678aee5dbc2a15d45a3e01a9f8e9.googledrive.com/host/0B1ZiqBksUHNYbDZOTnhJd2J4ZkU/January%202008%20QP%20-%20M2%20OCR.pdf

I tried resolving

F= mgcos30
F =m * 9.8 * root3/2
F = 8.49mN

Yh I don't really understand what's going on any help is appreciated.

Reply 1

tavtavtav

As a hint, I believe it is a work done / energy question.

alright, to start off maybe. Try considering Work Done, and energies involved.

You'll find the KE lost = W.D. against friction + PE inc.
remember W.D. = f*s
set up an equation with the distance A-B as x and try to solve.

Also message again if you get stuck.

(edited 7 years ago)

Reply 2

Super199

Original post by tavtavtav

As a hint, I believe it is a work done / energy question.

Yh I don't get it sorry. How am I supposed to be using energies here?
Wd= force * distance
How do I get the wd? Im assuming the force is found by what I did?

Reply 3

tavtavtav

Original post by Super199

Yh I don't get it sorry. How am I supposed to be using energies here?
Wd= force * distance
How do I get the wd? Im assuming the force is found by what I did?

work done is force by distance. so you need to multiply that force by the distance, the distance is unknown so we'll call it x

KE lost = GPE increase + WD against friction

so work out the KE lost and make it = to GPE increase in terms of x + wd in terms of x.

you can then solve for x.

remember GPE = mass * gravity * height

edit: extra hint in case you come back.

Spoiler

(edited 7 years ago)