M1 Questions!

Hey people, could you pls help me out with these two questions from the M1 book, review exercise 2? Thanks!

3)A particle P of mass 7m is placed on a rough horizontal table, the coefficient of friction between P and the table being m. A force of magnitude 2mg, acting upwards at an acute angle a to the horizontal, is applied to P and equilibrium is on the point of being broken by the particle sliding on the table. Given that tan a = 5/12, find the value of m.

4)A book is placed on a desk lid which is slowly tilted. Given that the book begins to slide when the inclination of the lid to the horizontal is 30 degrees, find the coefficient of friction between the book and the desk lid. State an assumption you have made about the book when forming the mathematical model you used to solve part a.

Reply 1

massimo

)A book is placed on a desk lid which is slowly tilted. Given that the book begins to slide when the inclination of the lid to the horizontal is 30 degrees, find the coefficient of friction between the book and the desk lid. State an assumption you have made about the book when forming the mathematical model you used to solve part a.

R=mgcos*
F=mgsin*
F=uR

Reply 2

lost_hamster

massimo

R=mgcos*
F=mgsin*
F=uR

Thanks, but im kinda confused? :redface:

Reply 3

massimo

4)A book is placed on a desk lid which is slowly tilted. Given that the book begins to slide when the inclination of the lid to the horizontal is 30 degrees, find the coefficient of friction between the book and the desk lid. State an assumption you have made about the book when forming the mathematical model you used to solve part a.

you need to split up the resultant force of thebook which is acting down on the plane !!

you do this by doing 9.8mSin30 this will give you F
so F=9.8mSin30 which is 4.9m (sin30=0.5)

then R is the perpendicular force of the book on the plane hence
R=9.8mCos30 so we have two equations

4.9m=9.8mCos30 m's cancel out

4.9=u(9.8Cos30)
so coeffeienct of friction is 4.9/(9.8cos30)

Reply 4

massimo

)A particle P of mass 7m is placed on a rough horizontal table, the coefficient of friction between P and the table being m. A force of magnitude 2mg, acting upwards at an acute angle a to the horizontal, is applied to P and equilibrium is on the point of being broken by the particle sliding on the table. Given that tan a = 5/12, find the value of m

i assume the force acting upwards is the same angle as the slope you will have to do tan 5/12 for me as i dont know what the angle will be but if you punch this lot into you calc you should get the right answer

p=2mgcos(angel)-F=0
R=7m-2mgsin(angel) (multiplied by the co effient of friction which is m) and F=R

anyway let me know how it goes and dont forget the postive rep thanks :wink:

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