a 100 kg car enters a level curve at 20m/s. if the curve has a radius of 80 m, what centripetal force must be applied by friction to keep the car from skidding?

It really doesn't matter for any of the questions that you've listed.

Question 1 answer: make sure you eat healthy foods and excercise atleast once a day.question 2 answer: sometimes bullying . bullying lowers a persons self-esteem sometimes which can make them not care for themselves to much making them feel bad about there body structer. that or they just have a bad body structer and there family/doctor said its unhealthy how they eat.