A bus travels 2800m south along a straight path with an avg. velocity of 24m/s to the south. The bus stops for 24 min., then it travels2100 m south w/average velocity of 20.8 m/s to the south. How long does the total trip last? What is the average velocity for the total trip?

Question

anonymous · Answer

I have two answers the first one 16 hrs and 26 minutes and the second one172.19 m/s but i don't know if it is right, please help :(

shane_b · Answer

As with any physics problem, once you've calculated the answer you should always ask yourself: does my answer make sense?  It shouldn't make sense that it would take *hours* to go 2800m if you're moving at an average velocity of over 20 m/s...even with a 24 minute delay.

Ok, let's work through it. Start by seeing how long the bus to do each leg:

$$t_1=\frac{2800m}{24m/s}=116.67s$$$$t_2=\frac{2100m}{20.8m/s}=100.96s$$$$t_3=24min==>24min*60s/min=1440s$$
How long does the total trip last?$$t_{total}=t_1+t_2+t_3=116.67s+100.96s+1440s=1657.63s$$
What is the average velocity for the total trip?

The average velocity will be the total displacement divided by the time it took to make the trip:$$\frac{2800m+2100m}{1657.63s}=2.96m/s$$That should sound about right...since the bus spent most of the trip at the bus stop.

<Note that you'll have to adjust the calcs to account for significant figures>