## anonymous one year ago Can somebody please help me with the following question: A book of mass 0.40 kg rests on a horizontal surface with which it has a coefficient of dynamic  friction of 0.50.    If this book is now pushed by an external horizontal force of 10 N, what will be its acceleration  immediately after it has started to move?     [Assume the gravitational field strength is 10 Nkg­1, that air resistance is negligible and that the  orientation of the book does not change.]

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1. anonymous

Try to start with a free body diagram of the book in the instant it starts to move. What are the forces applied on it at that moment?

2. anonymous

With your advice and some help from a textbook I think I have managed to come to an answer. I think its 20ms^-2 if I am not mistaken. Does anyone else agree?

3. anonymous

I get exactly the same value for the acceleration :) good work!

4. Michele_Laino

hint: here is the situation described in your exercise: |dw:1434687875634:dw| so we can write the subsequent vector equation: $\Large {\mathbf{F}} + {\mathbf{R}} = m{\mathbf{a}}$ where ${\mathbf{R}}$ is the friction force, namely: $\Large R = {\mu _D}mg$ and $\Large {\mu _D}$ is the dinamic friction coefficient. Now we can rewrite that equation in scalar form, so we get: $\Large F - {\mu _D}mg = ma$ please solve for a, and you will get your answer