A 15kg box is resting on a hill forming an angle of a horizontal surface. The coefficient of static friction for the box on the surface is 0.45. Calculate the maximum angle of the incline just before the box starts to move.

Answer 1

Let A be the angle.

Friction force = Weight component down incline

M g * cos A * 0.45 = M g sinA

solve for A.
Mg cancels out. (Use arctangent function)

Answer 2

27

Answer 3

Both of the answers above are wrong answer is 24°