posted by micole .
A 2.0kg box rests on a plank that is inclined at an angle of 65° above the horizontal. The upper end of the box is attached to a spring with a force constant of 25 N/m. If the coefficient of static friction between the box and the plank is 0.17, what is the maximum amount the spring can be stretched and the box remain at rest?
I thought I would use:
Max force of static friction= coefficient static x magnitude of normal force
But I am not sure how the angle comes into play? Also, how do I determine the normal force?