Solving Rotational Dynamics Problems | 20kg Cylinder, 10kg Cylinder

[vijay123]

dear guys,
i am very depressed since i cannot do these problems...please help me with them..
1)a solid cylinder of mass 20kg and radius 0.12m rotating with initial angular speed of 125ms-2 is placed lightly(ie without any translational push) on a horizontal table with co-efficient of kinectic energy of mu=0.15, between the cylinder and the table.
a)after how long does the cylinder start rolling?
b) what is the intial translational energy, rotational energy and the total energy of cylinder.

2)a cylinder of mass 10kg and radius 15cm is rolling perfectly on a plane of inclination 30degress. the coeffeicient of static friction is mu=0.25.
a)how much is the force of friction acting on the cylinder.

 

[Ukitake Jyuushirou]

ur suppose to have done the work urself otherwise the physics expert in the forum won't help u

 

[vijay123]

oh...ok fine..
here is how it goes...if you see the graph of static and kinetic friction, the line will slowly climb up until it reaches a certain point, known as static friction. so, in order to find the time, in which direction should the frictional torque be held?

 

[vijay123]

i don't know about rolling, does it mean that the accelartaion is zero and the net torique is zero?

 

[maverick280857]

Not at all, you sure need to read rolling before you can work on this problem. If you have Resnick&Halliday then the chapter on Rotational Kinematics followed by a section on Rotational Dynamics can be read.

The following links might be of some help:

http://hyperphysics.phy-astr.gsu.edu/hbase/rotwe.html#ro

http://hyperphysics.phy-astr.gsu.edu/hbase/circ.html#rotcon

http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html