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