[填空题]
When you are running and wa49 or/sfro )vo6v7;p0lqfe qz nt to stop quickly, you must decelrh ui:wxyc.1q ou63* xerate quickly. (a) What is the origin of the force that causes you to stop? (b) Estimate (using your own experience) the maximum rate of deceleration of a person running at toq uywuix o6*1.hxr c:3p speed to come to rest. m/s$^2$
