How Do You Calculate Average Speed from Displacement-Time Data?

[CedarPointer]

Homework Statement

Use the data table of displacement time data to get a line of best fit using your Ti-83 calculator. Once you have the equation, graph it so that you can answer the questions 1-5 that follow. Assume that the data below is for an object that is launched vertically upwards.

Time (sec) Displacment (m)
0 9.3
.5 15.075
1.0 18.8
1.5 20.475
2.0 20.1

Using the information above, calculate the average speed for the object from 0.75 sec to 2.9 sec.

Homework Equations

I've tried using the distance divided by time, but that hasn't worked, so I think the equation is actually where my problem is. The one I've tried mainly is average speed=change in distance/change in time

The Attempt at a Solution

Time Displacement
.75 17.193
2.9 14.259

AS=(14.259-17.193)/(2.9-.75)
AS= -1.36
Which isn't right.

Thanks!

 

[BruceW]

I think your calculation is correct. So maybe there is something wrong with using the calculator's line of best fit as a model for the displacement against time?

 

[CedarPointer]

I think the calculation might be wrong since -1.36 was correct as the answer for average velocity.

 

[Redbelly98]

This hint might help: Speed can never be negative. You need to know the distance (not displacement) traveled during the time interval.

p.s. Would your username be a reference to Cedar Point in Sandusky, Ohio?

 

[asteriatic]

The equation you are using, average speed = change in distance/change in time, is correct. However, the values you have used for change in distance and change in time are not correct. In order to calculate average speed, you need to find the total distance travelled and the total time taken.

To find the total distance travelled, you need to use the displacement values in the table and add them up. In this case, the total distance travelled would be 20.1 meters.

To find the total time taken, you can subtract the starting time from the ending time. In this case, the total time taken would be 2.9 seconds - 0.75 seconds = 2.15 seconds.

Now, you can plug in these values into the equation:
Average speed = (total distance travelled)/(total time taken)
= 20.1 meters/2.15 seconds
= 9.35 m/s

Therefore, the average speed of the object from 0.75 seconds to 2.9 seconds is 9.35 m/s.