What is the Average Speed of a Car on a 100 Minute Trip?

[cmkc109]

Homework Statement

A car travels at a speed v (km/h) for 40 minutes, then at a speed v/2 for 40 minutes, and finally at a speed v/3 for 20 minutes. What is the average speed for the trip

Homework Equations

avg v = displacement / time

The Attempt at a Solution

40v + 20v + 20/3 v = displacement
time = 40+ 40+ 20 = 100minutes

The answer given is 33.33
but, how do you cancel out the v.. I'm confused :(

 

[gclack1]

the average velocity is (5/9)*v

 

[gclack1]

what are the units of the 33.33

 

[cmkc109]

i don't remember :/ but in general, how to solve this question?

 

[gclack1]

you can't eliminate the v unless it gives you a value for it. the only thing i can think of is that 33.33 is the average time per journey of the car. if it is asking for the average speed then v must have been 60 km/h.