80 N at 30 deg means 2/3 of 80 N is to the side and 1/3 upwards. Take away 100 N and you are left with the downwards and sideways forces. Friction will be in the opposite direction to the sum of these forces. Drawing a scale diagram of this will help. Once you have worked out the overall force (downwards and to the side) you can calculate the acceleration in that direction by F = ma. You have just calculated the force and its direction and the mass is from 100 N divide by g (whatever value you should use depending on rounding).
Oct 26th, 2014
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