Problem 2-62 - Distance and speed - Part 6 (b)

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

\(\text{speed} = \frac{d}{\Delta t} \\ d = \text{(speed)} \Delta t \\ d_1 = 40\; km \\ d_2 = 90 \;km \\ d = 90 + 40 = 130\; km \text{(Answer to part (a))}\)

Correct!

Two significant figures
\(d = 90 + 40 = 130\; km\)

The average speed is:

(A)    \([40/(1/2)] + 90/1.5 = 80 + 60 = 140\; km/hr\)

(B)   \((1.3 \times 10^2\; km)/2\; hr = 65\; km/hr\)