# 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.

$\mathrm{d_1 = 40\; km}$

Continue.