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1. Hi, I am having serious trouble with this M2 Work,energy and power question:

A book slides down a rough desk lid which is inclined 30 degrees to the horizontal and falls to the ground which is 0.8m below the edge of the lid. The coefficient of friction between the book and the lid is 0.25. Given that the book starts from rest 0.4m from the bottom of the lid which is hinged at the edge of the desk, find the speed with which the book hits the floor.

The answer is 4.23 m/s. Any help would be appreciated!
2. use
Potential energy = Kinetic energy + work done against friction

ke = 0.5 mv^2

pe = mg(0.4sin30 + 0.8)

wd= friction force x distance = 0.25xmgcos30 x 0.4

put all that in, rearrange and you shoud get v = 4.23

Hope that helps!
3. thank you so much I understand it now

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