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January 30, 2015

January 30, 2015

Posted by **Jeremy** on Thursday, March 7, 2013 at 1:44am.

For example: the question was if i toss a ball in the air, and the Distance =0 (as a ball comes back to the ground and tossed from the ground), Time= 2 seconds, and acceleration = -10m/s^2. What is the initial velocity?

I tried using the Change in Velocity= Acceleration x Time. which should work because i am given acceleration and time. My working out is:

Vfin-Vini = -10m/s^2 x 2seconds

vfin=0 - Vini= -20

vini= 20m/s

But apparently the correct way to answer this question is to use this formula : Change in D= Vinitial x time + acceleration x Time ^2/2. Which works out to be 10m/s

If anyone could please tell me when it is appropriate to use each formula. OR where i have gone wrong in this please let me know

- Physics -
**drwls**, Thursday, March 7, 2013 at 8:08amThe final velocity (after 2 seconds) is not 0. It is zero after 1 second, at the top of the trajectory. That is why you got the wrong answer the first way.

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