The given question states that.
N atoms of a perfect gas are contained in a cylinder with insulating
walls, closed at one end by a piston. The initial volume is V and the initial
temperature T.
(a)Find the change in temperature, pressure and entropy that would
occur if the volume were suddenly increased to V2 by withdrawing the
piston.

Now the given solution says that
The gas does no work when the piston is withdrawn rapidly. Also,
the walls are thermally insulating, so that the internal energy of the gas
does not change, i.e., dU = 0. Since the internal energy of an ideal gas is
only dependent upon temperature T, the change in temperature is 0, i.e.,
Tz = TI. As for the pressure, p2/p1 = Vl/V2.

I was really puzzled by the given solutions, first of all it says that the gas does no work, I am not sure how this is possible if the volume is changing, second it says that as the walls are thermally insulating the internal energy does not change, I am pretty sure that thermally insulated walls imply that dQ=0, not dU=0.

The given problem is from MIT, I am really not sure what is going on