Question

if force = mass × acceleration then how does a car going at a constant speed (a = 0) exert a force on a pedestrian on impact?

Answer 1

force is also equal to mass * v-u/t.
where v=0 but u must have some velocity. consider initial velocity to be 30 m/s and final velocity is 0 and consider mass as 100 kg and time 10 second do
then equation becomes force = mass*v-u/t
force=100*30-0/10
=3000/10
=300 Newton