I haven't done an interview at loghborough but I did one at Oxford for mechanical engineering, can't imagine them being that different.
in first interview I was asked why I want to be an engineer, but I think it was just a warm up question. they also asked about my PS a bit but not much. Then they dove into a physics question which was mainly based upon circular motion; he explained at the start that I wasn't meant to be able to do it without guidance and whenever I got stuck they suggested stuff like 'does that look farmiliar'. I suggest anyone applying learns their formula booklet for mechanical subjects. Then I got asked to graph a couple things, so definelty be confident in that.
My second I kept making stupid mistakes, but they gave me time to correct myself. I got asked an energy question and then to plot the graphs
overall, I'd say be confident in mechanics questions (IE circular motion and energy questions) and graph plotting. also go over ur PS one more time. as to what to wear, go smart casual. I would not go in a suit but that's personal preference. most places don't care about what you wear it's about how you answer the questions.
good luck xxx