Mechnics slope question

kasheee · **Joined:** Thu, 16 Sep 2004 10:35:11 UTC **Posts:** 545

A block of mass 5kg, which may be modelled as a particle, is on a smooth slope which is at an angle of 30 degrees to the horizontal. It is held in equilibrium by a fore P Newtons which is at 20 degrees to the horizontal.

Find P.
It is the bit about 30 degrees to the horizontal I am confused about. I am used to questions where the angle given is relative to the slope. Could some help me please and give me a start with regards to the calculations.

Thanks.

kasheee · **Joined:** Thu, 16 Sep 2004 10:35:11 UTC **Posts:** 545

Perhaps give a sketch as well please.

outermeasure · **Posted:** Wed, 8 Aug 2012 16:23:52 UTC

kasheee wrote:

A block of mass 5kg, which may be modelled as a particle, is on a smooth slope which is at an angle of 30 degrees to the horizontal. It is held in equilibrium by a fore P Newtons which is at 20 degrees to the horizontal.

Find P.
It is the bit about 30 degrees to the horizontal I am confused about. I am used to questions where the angle given is relative to the slope. Could some help me please and give me a start with regards to the calculations.

Thanks.

kasheee wrote:

Perhaps give a sketch as well please.

The question is ambiguous as to whether P is pushing down or up vertically.

Resolve horizontally and vertically,
$\begin{aligned} P\cos 20^\circ-R\sin 30^\circ&=0\\ \pm P\sin 20^\circ+R\cos 30^\circ-5g&=0 \end{aligned}$
where R is the normal reaction force.

kasheee · **Joined:** Thu, 16 Sep 2004 10:35:11 UTC **Posts:** 545

Sorry, 20 degrees to the horizontal such that it pushes the block up the slope.I have the advantage of the diagram f the question in from of me.

Shadow · **Posted:** Thu, 9 Aug 2012 18:53:27 UTC

kasheee wrote:

Sorry, 20 degrees to the horizontal such that it pushes the block up the slope.I have the advantage of the diagram f the question in from of me.

If you like, for future posts you can attach an image if you upload it to some site which hosts images by using our

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Mechnics slope question

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