Posted by **Millie** on Sunday, October 2, 2011 at 5:23pm.

Two stones are thrown vertically up at the same time. The first stone is thrown with an initial velocity of 12.5 m/s from a 12th-floor balcony of a building and hits the ground after 4.6 s. With what initial velocity should the second stone be thrown from a 4th-floor balcony so that it hits the ground at the same time as the first stone? Assume equal height floors, and that in each case the stone is dropped from the same height as the ceiling.

- physics -
**bobpursley**, Sunday, October 2, 2011 at 5:33pm
time is the same.

first stone

hf=hi+vi*t-1/2 g t^2

figure the height of reach floor, and simplify the equation in this form

0=hi+vi*t-1/2 g t^2

second stone

or -hi=vi*t-1/2 g t^2

second stone> do the same thing, you should get

- hi*1/3=V*t-1/2 g t^2

or -hi=3V*t-3/2 g t^2

set the first and second equation equal

and do some algebra to get

t(3V-vi)=1/2 gt^2(3-1) and check that (I did it in my head).

YOu know t, vi, g, solve for V

check my head algebra.

- physics -
**Millie**, Sunday, October 2, 2011 at 7:59pm
I'm really confused by this. What am i supposed to use for t in the first equation if i only know that t going up is t and t going down is 4-t. I can't find two variables with one equation and the first equation is solving for hf.

## Answer this Question

## Related Questions

physics - Two stones are thrown vertically up at the same time. The first stone ...

physics - Two stones are thrown vertically up at the same time. The first stone ...

Physics - A stone is thrown up vertically from the ground (the gravitational ...

physics - A stone is dropped from the roof of a building; 1.60s after that, a ...

Physics !! - 1) A stone is dropped from the roof of a building; 2.00 s after ...

Physics - A stone is dropped from rest from the roof of a 100-m high building; 2...

physics - A stone is dropped from a 75 m high building. when this stone has ...

physics - A stone is dropped from a 75 m high building. when this stone has ...

Physics - Two stones are thrown vertically up with initial velocity Vo, second ...

Physics - a stone is dropped from a 75m building. when a stone has dropped 15m, ...