when we consider pure rolling on rough surface there is loss of K.E . the point of contact moves backward relative to the ground therefore friction acts forward , there is displacement of center of mass in the x direction (forward),yet the work done by friction is considered zero why ?????????

Dear Aditya,

Ans:- You have some misconceptions. The force of friction in case of pure rolling acts backward. This actually helps the body to rotate. The workdone against the force of friction is converted into the rotational KE. So in linear motion work done against the force of friction is lost but in the case of the rotational motion tha work done against the force of friction is converted into the rotational kinetic energy.

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SOUMYAJIT IIT_KHARAGPUR

how can any real force opposite in direction of relative motion help in relative motion. do u mean to say the sphere (RIGID BODY)will not pure roll for ever ?? ur wrong , the friction at the contact point acts forward and helps rolling ... the sphere will roll forever.

for pure rolling the friction acting is zero.

It neither acts in forward direction nor backward unless you have applied some external force.

In case of pure rolling the friction acting is zero.

It neither acts forward nor backward, unless there is some external force acting the body.