Problem 1A-1: Average Speed

At time t = 0 a car starts to move from point A along a horizontal line across as shown in the picture. Three more measuring points, B, C and D are set up along the line. The distances of those additional points from point A and the time when the car passes them are tabulated as follows:

Measuring points A B C D
Distance from point A, in kilometers (km) 0.00 0.10 0.50 1.50
Time the car passes, in minutes (min) 0.00 0.50 1.50 3.00
What is the average speed of the car between A and B, and between C and D? Express the answers in km/min, km/hour, and mile/hour, using the conversion 1 mile = 1.61 km.






Scroll down for solution













Solution:

Speed is defined as distance ÷ time.

The average speed from A to B = (0.10 - 0 km)÷(0.50 - 0 min)
                              = (0.10 km)÷(0.50 min) = 0.20 km/min
                              = (0.10 km)÷((0.50 min)÷(60 min/hr)) = (0.1×60÷0.50  km/hr)
                              = 12.0 km/hr
                              =  ((12.0 km/hr)÷(1.61 km/mile)) =7.45 mile/hr.

The average speed from C to D = (1.50 - 0.50 km)÷(3.00 - 1.50 min)
                              = (1.00 km)÷(1.50 min) = 0.67 km/min.
                              = (1.00 km)÷((1.50 min)÷(60 min/hr))
                              = (1.00×60÷1.50 km/hr)
                              = 40.0 km/hr.
                              = ((40.0 km/hr)÷(1.61 km/mile)) =24.8 mile/hr.

<-Previous page Table of contentsNext page->