- #1

Gui

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## Homework Statement

Problem (this is an extra credit challenge kinda thing): You kick a 2kg ball with 50N of force, directly upwards. The ball is not moving when you kick it. How far does it go and how long is it in the air (take gravity into consideration)?

## Homework Equations

I don't know, but I've been discussing this on #physics at freenode and 2 equation have been proposed although we haven't managed to figure it out yet: a = a0 - g*t AND v = v0 + at

I'm not sure whether each of them is right or not, but it's been tossed around and discussed. I've also been told I don't have enough information, but my teacher told me I did.

## The Attempt at a Solution

First, I tried this:

force = 50N

mass = 2kg

acceleration = ? = 25 m/s/s

gravity = 9.8 m/s/s

a = a0 - g*t (the second derivative of position equation x = x0 + vt+at^2/2)

a = 0m/s/s (the acceleration at the top when it stops)

a0 = 25m/s/s (the initial acceleration i got from f=m*a)

g = 9.8m/s/s

t = ?

0m/s/s = 25m/s/s - 9.8m/s/s*t

t = 2.551

Then I was told: "Wait a sec... what are you dealing with change in acceleration for" ... " your equation is incorrect ... your equation has acceleration confused with velocity"

So I tried this:

force = 50N

mass = 2kg

acceleration = ? = 25 m/s/s

gravity = 9.8 m/s/s

v = v0 + at (derivative of vf - vi = at)

v = 0 (final velocity, at the top when it stops)

v0 =

I'm not sure what to do from now on though. Any help is appreciated - thanks! :D