1. The problem statement, all variables and given/known data A 5.00-kg block is held at rest against a vertical wall by a horizontal force of 100 N. (a) What is the frictional force exerted by the wall on the block? (b) What is the minimum horizontal force needed to prevent the block from falling if the static coefficient of friction between the wall and the block is 0.400? 2. Relevant equations F=ma FS=FNμS 3. The attempt at a solution (a) Taking the normal force on the block to be 100 N, the frictional force should be 100μS or 40.0 N. This answer is wrong. Where am I screwing up? I probably shouldn't need μS for this part since it isn't given to me until part (b). (b) 5.00g-FS=5.00g-FN*0.400=0, so FN=123. N. This answer is correct, but if the block is held at rest by a force of 100 N, then how can that be? Any help would be much appreciated!