We know that, static friction force, fs=µsN where, µs is the coefficient of static friction and N is the normal force acting on the body. As the car is travelling on a circular track, so centripetal force is also acting on it. ⇒fC=
mv2
R
In limiting condition, fs=fC⇒µsN=
mv2
R
⇒N=
mv2
µsR
....(i) The magnitude of negative lift fL acting downwards on the car is given by fL=mg−N =mg−