Mechanics A level Edexcel Question Connected Particles

Could someone please help me on this question? I worked out the tension assuming that the motion was towards Q but the mark scheme had a different answer and they did assuming motion was towards P. I'm sure you're meant to have the same answer either way but I don't know where I am going wrong? Could someone please work out the tension assuming the motion is towards Q i.e. P is accelerating up the slope and Q is accelerating down? Thanks!


Two particles P of mass 6 kg and Q of mass 2 kg are connected by a light inextensible string. The string passes over a smooth pulley fixed at the top of a wedge.
One face of the wedge is smooth and inclined at an angle of 30° to the horizontal. The other face of the wedge is rough and inclined at an angle of 45° to the horizontal.
P lies on the smooth face and the string connecting the particles is taut. The coefficient of friction between Q and the rough face is 0.3.

I have attached the question and the mark scheme, when I find the tension (assuming motion is towards Q) I get 14.6N

I have attached the question and the mark scheme, when I find the tension (assuming motion is towards Q) I get 14.6N

Its obviously due to the sign of the friction term as your solution is in the opposite direction which will affect the behaviour.

Id think of it as a simple connected system with no friction to begin with and as, fairly trivially,
6g sin(30) > 2g sin(45)
then motion will be towards P and friction on Q will act down the slope. You have it acting up the slope.