velocity+avg. speed probs....help Pleassse!

[tangldupinBlue]

hey i'm confused with these problems. :bugeye: could anyone do a good deed and help me out? My teacher spends more time watching family guy than teaching us. thanks


1. a person walks first at a constant speed of 5.0 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.0 m/s (a) what is her average speed over the entire trip? (b) her average velocity over the entire trip?

2. A car makes a 200 km trip at an average speed of 40 km/h. A second car starting 1.0 h later arrives at their mutual destination at the same time. what was the average speed of the second car for the period that it was in motion?


thanks again. i don't really understand the first one--is it as simple as it seems? do you just divide 8.0/2 to get 4 m/s???? for average speed?

[recon]

1. (a) Call the distance between A and B x.

Then, the time taken to travel from A to B = Distance/Speed = \frac {x}{5}

The time taken to travel from B to A = \frac {x}{3}.

The total time taken to travel from A to B and back = \frac {x}{3} + \frac {x}{5}

The total distance travelled = 2x

Average Speed = Total Distance/Total Time

Work it out yourself. :smile:

(b) Since the person's displacement from his starting point is zero by the end of the journey, what do you think his velocity is? Have a look at your textbook for the definition of velocity.

2. First find the time taken to make a 200 km trip at 40 km/h. Then note that the second car takes 1 hour less than this. Remember that the distance travelled by both cars are equal.