Posted by sara on .
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

physics 
Anonymous,
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