# What equation should I use?

1. Nov 8, 2007

### get_rekd

how do you figure out how long it take's an object launched vertically upwards to reach its apex?
V=29.4 m/s

2. Nov 8, 2007

### aq1q

v(final)= Vo + a(t) (a= -9.8)

3. Nov 8, 2007

### get_rekd

so
-29.4 m/s = 29.4 m/s + -9.8t?

-58.8 m/s = -9.8t
----------- ------
-9.8 -9.8

6s = t to reach apex

Last edited: Nov 8, 2007
4. Nov 8, 2007

Vo is given

5. Nov 8, 2007

### aq1q

no when it reaches its apex (highest point), the ball has a speed of zero

6. Nov 8, 2007

### get_rekd

yeah so it is v(final)=29.4 m/s + a(t)
but doesn't an object come back down at the same velocity that it went up?
that is why I thought:
-29.4 m/s = 29.4 m/s + a(t)

7. Nov 8, 2007

### aq1q

right, thats true. but thats not what the question asks. It asks when it reaches its highest point, at the highest point the velocity is 0

8. Nov 8, 2007

### get_rekd

okay so then I should set final velocity to = 0 m/s?

0 m/s = 29.4 m/s + -9.8t
-29.4 m/s = -9.8 t
---------- -------
-9.8 -9.8

t = 3 s ?

9. Nov 8, 2007

### get_rekd

anybody?

10. Nov 8, 2007

### aq1q

yo, thats right

11. Nov 8, 2007

thanks