Question 7
In activity 02 the sandpaper on the bottom of the block is replaced with a rougher sheet, everything else being kept the same. What happens?
The right answer is the one marked above.
The limiting friction increases. A greater pull is now needed on the Newton balance before the block just begins to move.
Sticking on a different sheet of paper does not measurably change the weight of the block — and that is the point of the experiment, since a change in weight would have changed R as well.