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## Homework Statement

A crane is moving two equally spaced masses to the roof. One box is 10kg and the other box is 20kg. As the plank tilts towards the 20kg box, at what angle will each box begin to slide? The coefficient of static friction is 0.4

## Homework Equations

Newton's second law, Fnet=ma

## The Attempt at a Solution

Originally I thought I had correctly solved it, by simply setting Fnet=0 and solving for theta, however I didn't realize that the force of friction also depended on the angle, which I hadn't solved for. I ended up with this and I'm unsure of how to continue. Am I also correct in assuming both boxes will move at the same time?

Fnet=mgsinθ-Ff

0=10(9.8)sinθ-0.4(mgcosθ)

Thanks.