How to find initial velocity?

Question

I have been working on a problem that is driving me nuts. Okay, here it is.

Say a ball is thrown past a window 15m above the street with a verticle speed of 10 m/s. If the ball was thrown from the street what is the initial speed.

I would gladly appreciate any help. Thanks in advance.

Answer 1

Use conservation of energy:

(1/2)*m*(v0)^2 = (1/2)*m*(v1)^2 + m*g*h

where m is mass, v0 is the initial velocity, v1 is the present velocity, h is the height, and g is gravity.  

The mass, m, cancels you know gravity, height, and the present velocity, so you can solve for the initial velocity.

Hope that is helpful.

Answer 2

initial velocity= final velocity/acceleration x time taken

Answer 3

I agree:

At the window:

the ball has potential energy: m*g*h= m*9.8*15m

and kinetic energy= 1/2*m*v^2=1/2*m*(10)^2

its initial energy was 1/2*m*vi^2

by conservation of energy:

1/2*m*vi^2=1/2*m*(10)^2+m*9.8*15

solving for vi:

answer:

vi=sqr(10^2 + 2 * 9.8 * 15)= 19.85 m/s

Answer 4

v=distance/time



hope this helps!