An object of mass m is sliding with speed vi at some instant across a level tabletop, with which its coefficient of kinetic friction is µ. it then moves through a distance d and comes to rest. which of the following equations for the speed vi is reasonable?
a) vi = v2µd
b) vi = v2µmgd
c) vi = v-2µmgd
d) vi = v-2µgd
e) vi = v2µgd