Rectilinear motion 1.A car travels at 40km/hr for 2hrs, at 50km/hr for the next 3 hrs and finally at 30km/hr for 1hr. Find; a. The total distance traveled by the car in km b. The average speed of the car in km/hr and m/s?

1 Answer
Steve J.
May 4, 2018

a. #260 "km"#
b. #43.3 "km"/"hrs" = 12 m/s#

Explanation:

a. In the 1st section, the car goes #(40"km")/cancel(hr) * 2cancel(hrs) = 80 "km"#
In the 2nd section, the car goes #(50"km")/cancel(hr) * 3cancel(hrs) = 150 "km"#
In the 3rd section, the car goes #(30"km")/cancel(hr) * 1cancel(hrs) = 30 "km"#

The sum of those sections is #(80+150+30) "km" = 260 "km"#

b. #"Average speed" = "total distance"/"total time"#. Total time in this problem is #6 "hrs"#, so

#"Average speed" = (260 km)/(6 "hrs") = 43.3 "km"/"hrs"#

Converting that to units of m/s:
#43.3 cancel(km)/cancel(hrs) * (1000 m)/(1 cancel(km)) * (1 cancel(hr))/(3600 s) =12 m/s#

I hope this helps,
Steve

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