Question
A heavy solid sphere is thrown on a horizontal rough surface with initial velocity u without rolling. What will be its speed, when it starts pure rolling motion
Joshi sir comment
for translational motion
0-μMg = Ma so a = -μg
so after time t velocity v = u-μgt (1)
for rotational motion
about centre, μMgr = Iα = 2Mr2α/5
so α = 5μg/2r
so ω = 0 + αt
so ω = 5μgt/2r (2)
for pure rolling
v = rω implies that u-μgt = r5μgt/2r
implies that u = 7μgt/2
so t = 2u/7μg
now put t in (1) for getting v