Finding average acceleration over an time interal

[lazyboi605]

Homework Statement

An object moving with a constant acceleration travels 13 m in 7.8 s. The acceleration is then changed and the object covers an additional 34 m in 1.7 s. What is the average acceleration of the object over the entire interval described?

Homework Equations

X_f1 = 1/2(v_o +v_f)t
a=(v_o +v_f)/t

The Attempt at a Solution

v_f1 =2(13)/7.8
v_o =2(34)(1.7) - 44.2
a = (115.6-44.2)9.5

im not sure how to solve this problem

 

[Newton V]

take it back to orginial equation... you can not break down like that...
here is my answer for you: 0.52m/s/s (starting at 0)
however please consider the starting speed...

 

[lazyboi605]

can you show me what equation u used?

 

[Newton V]

lol, this has nothing to do with acceleration equation...
you just simply add 2 total distance together and divid them by total time to get average v, then v/t=a

 

[lazyboi605]

if u add the total distance and time, you only get an average velocity of one interval. The motion changes velocity.

 

[Newton V]

do you mean average accerleration over entire time or something else? i am not quit getting it...

 

[lazyboi605]

average acceleration over the entire interval

 

[Newton V]

then my answer should be right...

 

[Newton V]

you said average...

 

[lazyboi605]

i solved it. by finding the first velocity d/t. then the second velocity is 2(d₂/t₂) - v₁. then acceleration is v_f - v_o over time

 

[Newton V]

dude i told you...