Which of these is an example of acceleration?

a. a car maintains a constant speed of 40 km/hr.
b. a car is parked on the side of the road.
c. a speeding car brakes to a stop.
d. a car maintains a constant speed of 100 km/hr.

Which of the following correctly describes what happens when an atomic bomb explodes? small pieces of fissionable material are joined and form a body with a mass greater than the critical mass, the relative number of neutrons escaping decreases, and a chain reaction and explosion result. large pieces of fissionable matter are brought together quickly and form a body with a mass smaller than the critical mass, the relative number of escaping neutrons increases, and a chain reaction and explosion result.