A roller-coaster car at an amusement park has a mass of 1200 $\mathrm{kg}$ when fully loaded with passengers. As the car passes over the top of a circular hill of radius $18 \mathrm{m},$ assume that its speed is not changing. At the top of the hill, what are the (a) magnitude $F_{N}$ and (b) direction (up or down) of the normal force on the car from the track if the car's speed is $v=11 \mathrm{m} / \mathrm{s} ?$ What are $(\mathrm{c}) F_{N}$ and (d) the direction if $v=14 \mathrm{m} / \mathrm{s} ?$