Question 5
A block of weight 30 N rests on a horizontal table. Nothing else pushes or pulls it vertically. What is the normal reaction of the table on the block?
The right answer is the one marked above.
30 N. The block presses down on the table with a force equal to its weight, and by the third law the table pushes back with an equal and opposite force.
300 N comes from multiplying by g, but 30 N is already a weight — a force in newtons. Multiplying it by g again would give something that is not a force at all.