Jonah is trying to move his 22-kg desk by pushing on it with a force of 130 N, but his brother is leaning on it with a downward force of 24 N, just preventing it from moving. What is the coefficient of static friction between the desk and the floor?

0.54

Explanation:

Draw a free body diagram. There are 5 forces on the desk:

Weight force mg pulling down

Applied force 24 N pushing down

Normal force Fn pushing up

Applied force 130 N pushing right

Friction force Fnμ pushing left

Sum of the forces in the y direction:

∑F = ma

Fn - mg - 24 = 0

Fn = mg + 24

Fn = (22) (9.8) + 24

Fn = 240

Sum of the forces in the x direction:

∑F = ma

130 - Fnμ = 0

Fnμ = 130

μ = 130 / Fn

μ = 130 / 240

μ = 0.54