A string pulls a 9 kg box horizontally across a table with a force of 50 N. the box has a coefficient of friction with the table of 0.45. what is the net force of the box?

A. 90 N

B. 40 N

C. 50 N

D. 10 N

D. 10 N

Explanation:

Draw a free body diagram of the box. There are four forces:

Normal force N pushing up.

Weight force mg pulling down.

Applied force P to the right.

Friction force Nμ to the left.

Sum of forces in the y direction:

∑F = ma

N - mg = 0

N = mg

Sum of forces in the x direction:

∑F = P - Nμ

∑F = P - mgμ

∑F = (50 N) - (9 kg) (9.8 m/s²) (0.45)

∑F ≈ 10 N