Basically have a nasty little mechanics problem that I cannot solve. It is as follows:

A pulley is attached to a ceiling, one end of its string is attached to a mass M1, the other end is attached to the centre of another pulley whose ends of its string are attached to the masses M2 and M3. The three masses M1, M2 and M3 have the values 4, 10 and 6 kg respectively. All pulleys are frictionless and the strings are massless. What are the tensions in all the strings and what are the accelerations of the masses?

This is what I did:

The primary pulley is the one attached to the ceiling, M1 and the other pulley. The tension in its string is Tp and the acceleration of M1 is ap.

So considering the mass M1 and using F=ma

Tp - M1g = M1ap ---(i)

And doing the same for the other end of the primary pulley

(M2 + M3)g - Tp = (M2 + M3)ap ---(ii)

(i)+(ii) and some rearranging gives:

ap = (g(M2 + M3) - M1g) / (M1 + M2 + M3)

When you plug in the numbers mass M1 accelerates with ap = 5.88 m/s^2 (up) and Tp = 62.72N

I then did the same thing for the secondary pulley and taking into account the acceleration ap I get Ts = 73.5N, accn of M2 = 8.33 m/s^2 (down) and accn of M3=3.43 m/s^2 (also down).

Great. Wrong...

Apparently Tp is actually 48N and ap is 2.2 m/s^2

My first guess is that modelling the secondary pulley as just another mass (M2 + M3) for equation (ii) is wrong. So does anybody have any ideas on how to approach this question correctly?

Homework? Can't help you with your classwork, sorry.

I thought you were allowed to help as in guide, point in the right direction etc not actually do it for me, which is not what I'm asking btw.

Can you put up a diagram of this somewhere? I am a bit rusty in mechanics since I haven't done these problems since school, so I am having visualizing the set up.

Yeah sorry should have thought of that. This is the diagram that came with the problem.

Cheers