100 POINTS!! PLEASE DONT ANSWER UNLESS YOU KNOW BOTH ANSWERS PLEASE.

If a bike hits a rock and suddenly stops, the rider flies over the handlebars due to ________.
A. absolute zero B. displacement C. inertia D. electromagnetic spectrum

During a track meet, Sarah ran 400m in 80s. What was her average speed? (Remember s=d/t)

A. 5 m/s

B. 20 m/s

C. 15 m/s

D. 15 mph