# Velocity+avg. speed probs help Pleassse!

1. Sep 21, 2004

### tangldupinBlue

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

hey i'm confused with these problems. 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?

2. Sep 21, 2004

### 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.

(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.

Last edited: Sep 21, 2004