F=m.a
=m(v-u)/t
(since v=o, a=-u/t)
v-u=d/t
-u=15/23
u=-0.65 m/s
F=m.-u/t
=52.5*0.65
=1.47 N
Conventionally, for the stopping force, F is taken to be negative. So, the stopping force is -1.47 N and this force is the frictional force and its direction is opposite to that of motion.