1、Today I drove 125 miles in 110 minutes.What was my` average speed in miles per hour?(There are 60 minutes in one hour)
Ans：average speed v=total course/time cost=125/(110/60)≈68.18 miles/hour
2、Light travels through space at a constant speed of 3X10⁸m/s.What is the acceleration of a beam of light?
Ans：Since the speed of a beam of light is a constant,the acceleration is zero(0).
3、what is the acceleration of a car if it begins at 100km/h and comes to a stop after 8 seconds?you may write your answer with the units of km/h/s.In what direction is the car's acceleration (in the same direction or opposite direction of the car's motion)?
Ans:the acceleration a=(0-100)/8=-12.5km/h/s
where "-" suggests that the acceleration is opposite the direction of the car's motion.
