Resolving Vector Components

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• Oct 19th 2009, 01:34 AM
unstopabl3
Thanks, that works fine when the questions are simple but when they have three or more forces acting upon an object I get confused as to how to draw the components and which one is horizontal and which one is vertical.

For example how would you solve the following question.

Q) The diagram shows a horizontal force of magnitude 30 N acting on a block of mass 2 kg, which is at rest on a plane inclined at 50 degrees to the horizontal. Find the magnitude and direction of the frictional force on the block.
• Oct 19th 2009, 02:33 AM
Quote:

Originally Posted by unstopabl3
Thanks, that works fine when the questions are simple but when they have three or more forces acting upon an object I get confused as to how to draw the components and which one is horizontal and which one is vertical.

For example how would you solve the following question.

Q) The diagram shows a horizontal force of magnitude 30 N acting on a block of mass 2 kg, which is at rest on a plane inclined at 50 degrees to the horizontal. Find the magnitude and direction of the frictional force on the block.

It's the same .

There are a few components in this question . The weight component , mgsin theta acting downwards , the force component acting upwards , and the frictional force acting downwards .

$F \cos \theta = F_r + mg\sin \theta$

$30\cos 50 = F_r+(2)(9.81)\sin 50$

$F_r=4.254$ N
• Oct 19th 2009, 07:44 AM
unstopabl3
Could you please explain step by step how you solved each component? I still don't get it :/

Also why is the friction force acting downwards? Shouldn't it be upwards considering it's a slop and the block has a tendency to falls downwards thus the friction in the opposite direction?

Please bare with me, this component thing along with friction and weight components is just not getting through me :( Please explain to me with diagrams on how you find each component for such questions.

Much appreciated!
• Oct 19th 2009, 08:31 AM
Quote:

Originally Posted by unstopabl3
Could you please explain step by step how you solved each component? I still don't get it :/

Also why is the friction force acting downwards? Shouldn't it be upwards considering it's a slop and the block has a tendency to falls downwards thus the friction in the opposite direction?

Please bare with me, this component thing along with friction and weight components is just not getting through me :( Please explain to me with diagrams on how you find each component for such questions.

Much appreciated!

once again , take a look at the diagram i attached . How would relate Fx with F ?

The force exerted on the mass is acting upwards so the frictional force acts downwards . Just a simple example would be using the sand paper . When you rub it forward , the resistance is backwards and vice versa .

For the weight component , you will need to resolve it also . W always acts downwards (exactly downwards) regardless of how the mass is placed .
• Oct 19th 2009, 08:40 AM
unstopabl3
I'll give it a try and let you know.
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