Posted by **Liz** on Wednesday, December 28, 2011 at 4:24pm.

If the mass is 4.3 kg, the initial speed is 4.0 m/s, and the initial height is 8.4 m, find the speed of the ball when it is at a height of 8.0 m.

Please and Thank You for the help.

- physics -
**Damon**, Wednesday, December 28, 2011 at 4:40pm
I assume it is going straight up.

v = 4 - 9.8 t

8 = 8.4 + 4 t - 4.9 t^2

you can solve the soecond for t with quadratic equation (take the positive t) and then use the first equation to find v

However it is easier to use energy

(1/2)m v^2 + m g h = constant

cancel m It does not matter, rock same as feather here.

(1/2)(4^2) + 9.8(8.4) = (1/2)v^2 + 9.8(8)

- physics -
**drwls**, Wednesday, December 28, 2011 at 4:42pm
In what direction is it launched? Straight down? It makes a dofference. The mass will not matter.

You may have omitted part of the question.

- physics -
**Damon**, Wednesday, December 28, 2011 at 4:44pm
I do not think it matters in the end if straight up or straight down, but at some intermediate angle is no good.

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