URGENT HELP:::A car accelerates at a constant rate from zero to 48.9 m/s in 10 seconds and then slows to 13.1 m/s in 5 seconds. What is its average acceleration to the nearest tenth of a m/s2 during the 15 seconds?
The answer is 0.9, WHY?

Question

URGENT HELP:::A car accelerates at a constant rate from zero to 48.9 m/s in 10 seconds and then slows to 13.1 m/s in 5 seconds. What is its average acceleration to the nearest tenth of a m/s2 during the 15 seconds? 
The answer is 0.9, WHY?

happykiddo · Answer

I used the formula
$$Average Acceleration= \Delta V / \Delta t$$

irishboy123 · Answer

for the whole journey what are

$$\Delta V$$   
$$\Delta t$$

irishboy123 · Answer

*whole* journey

happykiddo · Answer

delta V= 13.1m/s - 48.9 m/s
delta t= 5 s- 10s

irishboy123 · Answer

"at a constant rate from zero"

irishboy123 · Answer

"at a constant rate **from zero**"

irishboy123 · Answer

the journey started at t = 0

happykiddo · Answer

So are you saying to just use 15 seconds as my "t" value?

irishboy123 · Answer

yes!

irishboy123 · Answer

so does the question :p

"What is its average acceleration to the nearest tenth of a m/s2 **during the 15 seconds**"

happykiddo · Answer

I've already tried that it gives me -2.4.....not 0.9

irishboy123 · Answer

what speed did the journey start at?

what speed did the journey end at?

happykiddo · Answer

Alright I got the answer :P , feeling pretty stupid that i used 48.9 m/s as my initial velocity.  I appreciate the help. Thanks : )

irishboy123 · Answer

good job!  been there, done that myself :-)