MHB Particles on a Wedge Q4: Find Accel & Force

[markosheehan]

Q4 A wedge of mass 11 kg is held on the ground
with its base horizontal and smooth faces
inclined at 30° and 45° respectively to the
horizontal.
A 5 kg mass on the face inclined at 30° is
connected to a 7 kg mass on the other face by
a light inextensible string which passes over a
smooth light pulley.
The system is released from rest and the wedge does not move.
Find (i) the acceleration of the particles
(ii) the vertical force exerted on the ground.

i have the marking scheme to this question. here is the link http://thephysicsteacher.ie/Exam%20M...hemes/2015.pdf. it is question 6 part b. i don't understand how they work it out could someone explain it to me. first of all they use a for acceleration. what acceleration does this stand for the particle or the wedge. and if it stands for the particle why did they not resolve the acceleration parallel and perpindicular to the plane. why did they only use one acceleration . i learned to do these questions by always looking at both the acceleration of the particle and the wedge
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[I like Serena]

Q4 A wedge of mass 11 kg is held on the ground
with its base horizontal and smooth faces
inclined at 30° and 45° respectively to the
horizontal.
A 5 kg mass on the face inclined at 30° is
connected to a 7 kg mass on the other face by
a light inextensible string which passes over a
smooth light pulley.
The system is released from rest and the wedge does not move.
Find (i) the acceleration of the particles
(ii) the vertical force exerted on the ground.

i have the marking scheme to this question. here is the link http://thephysicsteacher.ie/Exam%20M...hemes/2015.pdf. it is question 6 part b. i don't understand how they work it out could someone explain it to me. first of all they use a for acceleration. what acceleration does this stand for the particle or the wedge. and if it stands for the particle why did they not resolve the acceleration parallel and perpindicular to the plane. why did they only use one acceleration . i learned to do these questions by always looking at both the acceleration of the particle and the wedge

Hi markosheehan!

I'm afraid your link does not work, so I can't comment on the marking scheme.

I can already say that since it says "the wedge does not move", $a$ won't refer to the wedge.
Instead $a$ would be the magnitude of the acceleration of one of the masses (or particles), which is the same as the acceleration on the other mass, since they're connected by an inextensible string.