Understanding Average Speed Calculations

[rcmango]

Homework Statement

there's a motorist that travels 30 miles at 60 mph, and another 60 miles at 30 mph.

Homework Equations

The Attempt at a Solution

The average speed of the motorist is 36 mph
how was this computed?

i know avg speed is distance / chng of time

however 30+ 60 divided by 60 + 30 is not 36.
need help.

 

[JasonRox]

Please write the full question.

 

[rcmango]

...nevermind i think it got it,

since he's traveling only half the distance of what speed he's going, then he probably only went about 30 minutes, and then the oppositive of that with the other, which is 2 hrs, then distance of 90 / 2.5 hrs is the avg speed of 36 m/s

thanks anyway.

 

[saket]

good!
just to, may be, boost up your knowledge:
can you tell, why v_average = (v₁ + v_[2)/2 is not applicable here? {Note, it would give 45mph}
Also, note that constant speed is provided in either part of the motion.