Need M1 help!

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202011%20-%20QP/6677_01_que_20110119.pdf

Q6 b.

I'm struggling to understand why friction is going down the slope. I was taught that to see which way the frictional force is acting, remove the friction and see which way the particle would go. The opposite of this direction is the direction of friction.

If there is no friction, surely the particle would roll down the slope? I calculated the reaction force to be 96 therefore Friction to be 48N. The answers say friction is going down the slope meaning I'm wrong. How do you tell which way Fr is going?

The exam is tomorrow lol,..

OP

anyone?

The particle remains in equilibrium. If you look the force is acting up the plane meaning that the force acting up must = friction and the mass of the particle's force. Friction is the opposite to the direction of motion so it must be acting down the plane. It wouldn't make sense as lets take for example a man was pushing that particle up the plane. He gives enough force for it to be in equilibrium. The force which is pulling it down however is it's mass and friction is acting down between the particle and the man pushing it up the plane? I know it's not a good example but think about it as friction always acts in the opposite of the direction unless told otherwise. I just did the question and got 120, I don't even understand how so little working out gets you 8 marks.

Reply 3

TenOfThem

18

Original post by lollage123

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202011%20-%20QP/6677_01_que_20110119.pdf

Q6 b.

I'm struggling to understand why friction is going down the slope. I was taught that to see which way the frictional force is acting, remove the friction and see which way the particle would go. The opposite of this direction is the direction of friction.

If there is no friction, surely the particle would roll down the slope? I calculated the reaction force to be 96 therefore Friction to be 48N. The answers say friction is going down the slope meaning I'm wrong. How do you tell which way Fr is going?

The exam is tomorrow lol,..

Your definition is correct but your assumption that the particle is about to slide down is incorrect

When P is at it's MAXIMUM it will be overcoming both gravity and friction