Q.
A particle moves on a rough horizontal ground with some initial velocity say v0. If (3/4)th of its kinetic energy is lost in friction in time t0, then coefficient of friction between the particle and the ground is:
3/4th energy is lost, i.e., 1/4th kinetic energy is left.
Hence, its velocity becomes v0/2 under a retardation of mmg in time t0. 2v0=v0−μgt0
or μ=2gt0v0