Posted by **sara** on Sunday, September 10, 2006 at 12:10pm.

A car travels on a straight road for 40km at 30km/h. It then continues in same direction for 40km at 60km/h.

a)What is the average velocity of the car during the 80km trip?(assume it moves in positive x direction)

b)What is the average speed?

c)graph and indicate how average velocity is fond on graph

a) I am confused when the car then changes its speed.

b)I forgot the equation for speed

c)Would I graph a position time graph and find out the area under the graph?

The confusion is this: Always, average speed is defined as

distance/time

distance= 40 km + 40 km

time= distance/vel= 40/30 + 40/60

avg speed= 80/(40/30 + 40/60)

in the case of going the same direction, avg speed = avg velocity

On the position time graph...

slope is veloicty. You know the veloicty for the first time of (40/30 hr), plot that line to that time. Then to the second line, starting at the end of the first.

You don't need area. For avg velocity, draw a line from the origin to the ned of the second line, and take the slope of that line....avg velocity= finalpositioin/time

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