Saturday
January 31, 2015

Homework Help: physics

Posted by Wes on Sunday, February 10, 2013 at 7:00pm.

A rock is dropped from a treetop 19.6 m high, and then,
1.00 s later, a second rock is thrown down. With what
initial velocity must the second rock be thrown if it is to
reach the ground at the same time as the first?

I'm not sure how to find the initial velocity of the thrown rock, since it's not 0

What I have so far:

1st rock:
Yo=o
Yf=19.6 m
Vo=o
Vf=
T=
A= -9.80 m/s^2

I think I've found the final velocity and time of the 1st rock
(Vf^2=Vo^2-2g(Y-Yo)
or final velocity squared = initial velocity(0 m/s)^2 -2(9.80)(-19.6-0)
which is = to -19.6 m/s
Time = 2 seconds
(Vf=Vo-gt, Vf/Vo-g=T, -19.6 m/s /-9.80 m/s^2, 2 seconds

How do I find the initial velocity of a throw object when I know:
Yo=o
Yf=19.6 m
T= 2-1 = 1 second
A- /9.80 m/s^2

Thanks!

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