I am not a big mechanic/physics guy so I might be totally wrong but I have a reasonable guess for this one. The fact that is is 9kg is irrelevent. What is relevent that the acceleration on an inclined plance is 4.9m/s2. While regular acceleration due to gravity is 9.8m/s2. Thus, it is reasonable to say it is half the angle of free fall. Since free fall happens at 90 degrees this one happens at 45 degrees.Originally Posted by Confuzzled?