# Kinematics (rectilnear motion) simple

1. Dec 22, 2013

### whynot314

Ball 1 is launched with an initial vertical velocity v1=160 ft/sec. Three seconds later, ball 2 is launched with an initial velocity v2. determine v2 if the balls are to collide at an altitude of 300ft.

not sure where I am going wrong, do I have my limits correct?[URL=http://s1341.photobucket.com/user/nebula-314/media/20131222_191532_zpsf76c1ab5.jpg.html][PLAIN]http://i1341.photobucket.com/albums/o745/nebula-314/20131222_191532_zpsf76c1ab5.jpg[/URL][/PLAIN]

2. Dec 22, 2013

### whynot314

v2 being initial velocity.

3. Dec 22, 2013

### Konoha

I'm not sure what you're doing here, but if I were you I would use the following equation to calculate t for the first ball to reach 300ft, then using that t minus 3 (because the 2nd ball was launch 3 seconds later) and the same equation I would calculate v2.

$\Delta$x= $\frac{1}{2}$a$t^{2}$+$v_{0}$t

Just remember that here we take upside direction to be positive, hence a=-g and if you are measuring distance in ft you should use g=32.17 ft/s^2 , or convert ft to meter and use g=9.8 m/s^2

Let me know how it goes :)

Last edited: Dec 22, 2013
4. Dec 23, 2013

### whynot314

Oh i was trying to derive that equation, and perhaps save some steps.

5. Dec 23, 2013

### whynot314

But your solution did help a lot thanks.

6. Dec 23, 2013

### Konoha

oh I see! I guess sometimes it's just easier to stick to the basics! :tongue2:

No problem at all, happy to help