Physics Kinematics question

[iceman132]

Tom has a 40 mile commute to work one-way. If he averages 60 miles per hour on the way there and 40 miles per hour on the way home, then what is his average speed for the round trip?

Answer is supposed to be 48 mph.

I don't see why it can't be 50 mph??

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[SeminoleVesicle]

Tom has a 40 mile commute to work one-way. If he averages 60 miles per hour on the way there and 40 miles per hour on the way home, then what is his average speed for the round trip?

Answer is supposed to be 48 mph.

I don't see why it can't be 50 mph??

It took him 40 minutes to get there one-way (40 miles/60 miles per hour), and one hour to get home. 40+60=100 minutes. 100 minutes/60 minutes per hour= 1.67 hrs.

He travels a total of 80 miles in 1.67 hrs. 80/1.67=(80x3)/5=48mph

P.S.: I heard Tom has a hot wife.

 

[iceman132]

It took him 40 minutes to get there one-way (40 miles/60 miles per hour), and one hour to get home. 40+60=100 minutes. 100 minutes/60 minutes per hour= 1.67 hrs.

He travels a total of 80 miles in 1.67 hrs. 80/1.67=(80x3)/5=48mph

P.S.: I heard Tom has a hot wife.

I see now. I got up to the 100 minutes but didn't know what to do with it.

Much appreciated!

 

[SeminoleVesicle]

I see now. I got up to the 100 minutes but didn't know what to do with it.

Much appreciated!

No problem, units are very important for the MCAT.