Friction force and train accelerating force are opposite
in direction and equal in magnitude. Therefore m x a = u x m x g
As the mass is same,
hence both are cancel out and remaining equation is
a = u x g
It’s given that a =
0.20g, so
0.20g = u x g
Cancel “g” on both
sides;
0.20 = u
Thus the coefficient
of static friction = u = 0.20
