A cylinder rolls up an inclined plane , reaches some height and then rolled down ( without slipping through out ) directions of friction during upward and downward motions are :
I think up the incline while climbing and down the incline while descending .coz
friction opposes relative motion while going up the part touching the incline will tend to move down so friction is up , while going down , the part touching will have a tendency to move up so friction acts downwards .
but answer given is both times upwards as the point of contact will be at rest so the cylinder has tendency to slide down the incline so friction acts upwards . mughe thoda doubt hai koi explain karo .plz
-
UP 0 DOWN 0 0 2
2 Answers
3THE MG SIN θ FORCE WILL TRY AND BRING DOWN THE VELOCITY ...........
BUTT THE W IS UNCHANGED[2].....
SO FRICTION ACTS IN SUCH A WAY SO AS TO INCRESE THE v AND DECREASE W....
SO CLEARLY IT ACTS UPWARD!!!!!!!!!!!!!! WHILE GOIN UP!!!!!!!!!!
BUT WHILE COMIN DOWN THE VELOCITY IS INCREASING DUE TO THE MG SINθ FORCE BUT W REMAINS SAME[2][3].......
SO THE FRICTION IN ACTS IN SUCH A WAY SO AS TO INCREASE W AND DECREASE v !!!!!
so clearly it acts upwards again!!!!!!!!!!!!!!!!!!!!!!!
so """wat is given"""" is perfectly rite .......................
and why does friction behave like this???????
its becuze it wants the cylinder to perform pure rollin!!!!!!!!!
and y does it want this ..............
so that the point of contact dosnt slip!!!!!!!!!!!
[1]
106When the cylinder rolls upwards:
the gravity opposes the motion and hence the velocity of centre of mass decreases so there should be a necessary torque to decrease the angular velocity. hence friction should act upwards as it produces the torque to reduce ang. vel.
When the cylinder rolls downwards:
the gravity acts downwards hence the velocity of center of mass increases hence the ang. vel. should also increase. So, friction should act upwards as it will produce the necessary torque to increase the ang. vel.
