A commuting student leaves home and drives to school at an average speed of 42.0

Question

A commuting student leaves home and drives to school at an average speed of 42.0 km/h. After 20.0 min he realizes that he has forgotten his homework and returns home to get it at the same average speed. It takes 8.0 min to find the report, after which the trip to school 42.0 km away to the east is resumed at the same speed as before.
What is the average speed for the entire trip ?

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C secure https://loncapa2 physics.sc.edu/res/scgblanpied/courses/usdiboneslib/chapter2 onesc2p20 problem?symbzuploaded%2fsc%2f903012791ea535ael scl1%2fdefault 1250914843 Nicholas Ballowe (Student section: 1) 2018 Sp, Phys 201 (wilson) Messages Courses Help Logout Main Menu Course Contents Course Contents » » HW 1 Average-speed-velocity Notes Bookmark Evaluate tCommunicate -Print e. Info Average-speed-velocity (C2p20) A commuting studet laves home and drives to school at an average speed of 42.0 km/h. After 20.0 min he realizes that he has forgotten his homework and returns home to get it at the same average speed. It takes 8.0 min to find the report, after which the trip to school 42.0 km away to the east is resumed at the same speed as before What is the average speed for the entire trip ? Submit Answer Tries 0/12 What is the average velocity for the entire trip? Submit Answer Tries 0/12 This discussion is closed Send Feedback 10:04 AM O Type here to search

Explanation / Answer

Average speed = total distance / total time

leg 1: time = 20 min = 20/60 hour or 0.333 hour   (way to school)

distance = 42 km/h x 0.333h = 14 km

leg 2: time = 0.333 hour, distance = 14 km (way back home)

leg 3: time = 8 min or 0.133 hour, distance = 0 (finding report)

leg 4: distance = 42 km, time = 1 hour (back to school)

total distance = 42+14+14 = 70 km

total time = 0.333+ 0.333+0.133+1= 1.799 hour

average speed = 70/1.799 = 38.91 km/h

average velocity = vector sum of distances / total time

taking direction towards school as +

and assuming all of the travel is in a straight line, no curves or angles

Distance total is 14–14+42 = 42 km

time total is the same, 1.799 hour

average velocity = 42/1.799 = 23.35 km/h

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