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## Homework Statement

A 800 N box was pushed up an incline plane of length 4.0m (measured along the incline) to a window ledge 2.0m above ground level. This process required that 3200J of work be done.

**What was the average frictional force along the plane?**

## Homework Equations

W=Fd

## The Attempt at a Solution

sin(theta) = 2/4

theta = 30 degrees

W = 800 N (4cos30)

W = 2771 J

W_friction = 3200 - 2771

= 429J

so the force done by friction would just be

429 = F(4cos30)

F = 124 N

This is wrong

the correct answer is 400 N

Thanks for any help :)