Magnitiude of normal force when given mass, force and friction

Question

You apply a force of 10.6 N horizontally to a 1105 g box that is at rest on a horizontal surface. The friction force between the box and table is 4.4 N. What is the magnitude of the normal force acting on the box?

Answer 1

If we draw a free body diagram it will look like this:

Since the box is at rest we know that the sum of the forces in each direction equal zero

10.6 - F_f = 0

W - F_N = 0

We want to find the normal force, so we can rewrite the second equation to get

W = F_N

Weight = mass * gravity

W = 1.105 (kg!, not grams) * 9.8

W = 10.829 N

Since W = F_N, the normal force also equals 10.829 N