$5.$ A roller coaster travels around a circular loop of radius R$.$ As it travels to the top of the loop, it reaches a speed of $(2$gR$)/2,$ where g is the gravitational acceleration on the surface of the Earth.

It travels subsequently toward the bottom of the loop. What is the normal force exerted on the passenger whose mass is m by the seat of the cart when the coaster arrives at the bottom of the cart, assuming that the wheels of the cart roll without slipping.

$5$ mg;

$6$ mg;

$7$ mg;

$8$ mg$.$