Posted by **Jennifer** on Wednesday, September 15, 2010 at 10:26pm.

A ball is thrown vertically upward with a

speed of 25.4 m/s from a height of 2.1 m. (Remember gravity is a=9.8m/s^2)

How long does the ball take to hit the ground after it reaches its highest point?

Answer in units of s.

- Physics -
**Angela**, Wednesday, September 15, 2010 at 10:38pm
make a parobala, find the highest point find the time for the whole thing, then dive the time in half. hope that kind of helped !

- Physics -
**drwls**, Wednesday, September 15, 2010 at 10:43pm
height Y = 2.1 + 25.5 t - 4.9 t^2

Solve for the time Y = 0

It reaches its highest point when t = Vo/g = 25.4/9.8 = 2.59 s

Since they want the time it takes to hit the ground AFTER reaching the highest point, you will need to subtract 2.59s from the time Y=0

There is another way to do this without solvoing a quadratic equation>

1) use conservation of energy to calculate how much higher high it goes.

g*(deltaY) = Vo^2/2

2) Add the initial elevation, 2.1 m, to delta Y. That will give you Ymax

3) T (time to fall from max height)

= sqrt (2 Ymax/g)

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