Average velocity during third second.

[seek_solutions]

How do I find the Average velocity during third second for a particle whose position is given by x = 5t^2 - 10 ?

I know average velocity = displacement/time

So At t = 0, position is - 10

t = 3, position is 35,

So displacement is 45, average velocity is 45/3

However that is wrong!! Help!

 

[skeeter]

t = 0 to t = 1 is the 1st second
t = 1 to t = 2 is the 2nd second
t = 2 to t = 3 is the 3rd second ... and so on.

for the 3rd second ...
v_avg = [x(3) - x(2)]/(3 - 2) = (35 - 10)/1 = 25

 

[stapel]

The question didn't ask for the average over the first, second, and third seconds; it asked only for the average over the third second.

Eliz.

 

[seek_solutions]

skeeter thanks for the enlightenment!

The full question:

The position of a particle is given by the relationship x = 5t^2 - 10 where x is the displacement in metres from a fixed origin after t seconds. For the particle find the average velocity during the third second.

skeeter is correct as his answer matches the answer i could not get, so now when the question asks for say "during the 4th second" it really means from 3rd to 4th.

Oh and sometimes it asks "Average velocity in the first 5 seconds". What do you do then? Take t = 0 and t = 5 and then average them? Thanks!

 

[skeeter]

Oh and sometimes it asks "Average velocity in the first 5 seconds". What do you do then? Take t = 0 and t = 5 and then average them? Thanks!

yes ... in the first five seconds, v<avg> = [x(5) - x(0)]/(5 - 0)