Problem 2-62 - Distance and speed - Part 4 (c)

A truck travels at \(80 \;km/h\) for \(30\; min\), then at \(60 \;km/h\) for \(1.5 \;hr.\) Assuming 2 significant digits in the given numbers, calculate the truck's
(a) total distance traveled, and
(b) average speed.

Accumulated Solution

\(\mathrm{speed = \frac{d}{\Delta t }\\ d = (speed) \Delta t \\ d_1 = 40\; km}\)


This shows the usefulness of including the units in the calculations. The choices should have been:

(A)    \(\mathrm{(80\; km/hr)(30\; min) = 2400\; km}\)

(B)    \(\mathrm{(80\; km/hr)/(30\; min) = 8/3\; km}\)

(C)    \(\mathrm{(80\; km/hr)(1/2\; hr) = 40\; km}\)

Now you can clearly see that A and B are incorrect.

\(\mathrm{d_1 = 40\; km}\)