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M1 help stuck :(

When resolving in the direction of the Reaction Force, why do you subtract 25cos80? It isnt revelant as it isnt in the similar direction??

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Reply 1

SherlockHolmes

Original post by naxiv

When resolving in the direction of the Reaction Force, why do you subtract 25cos80? It isnt revelant as it isnt in the similar direction??

The 25cos80 is the component of the 25N force applied that is perpendicular to the plane.

(edited 9 years ago)

Reply 2

Muttley79

We are resolving perpendicular to the plane.

The force 25N is not at right angles to the direction we are resolving in so a component of that force has to be considered.

Reply 3

naxiv

Dont understand can you make it simplier pls.

So resolve perp to the plane
Ie all force in the direction of R
So
R -2gcos10 = 0 ??

Original post by SherlockHolmes

The 25cos80 is the component of the 25N force applied that is perpendicular to the plane.

Original post by Muttley79

We are resolving perpendicular to the plane.

The force 25N is not at right angles to the direction we are resolving in so a component of that force has to be considered.

Reply 4

TenOfThem

Original post by naxiv

Dont understand can you make it simplier pls.

So resolve perp to the plane
Ie all force in the direction of R
So
R -2gcos10 = 0 ??

You are ignoring the 25N

This is not parallel to the slope so it needs to be resolved in the directions parallel and perpendicular to the plane

Reply 5

Muttley79

A component of the 25N is acting to hold the box on the plane i.e. opposite direction to the reaction force.

Maybe extending the line of 25N would help you see?

Reply 6

davros

Original post by naxiv

Dont understand can you make it simplier pls.

So resolve perp to the plane
Ie all force in the direction of R
So
R -2gcos10 = 0 ??

You can't ignore the 25N force!

The 25N force is horizontal - if you were resolving horizontally and vertically it would have no vertical component. However, you're not resolving horizontally and vertically, you're resolving parallel to the plane and perpendicular to the plane, and the 25N force has components in each of those directions!