Ball and Runner: Catching at the Bottom of a Building

[star20]

Homework Statement

A ball is thrown from top of a 25m tall building. The balls initail speed is 12m/s. At the same instant a person is running on the ground at the distance of 31m from the building. What must be the avg speed of the person if he is to catch the ball at the bottem of the building?

Homework Equations

Ball
V initial = +12m/s
x= 25m
t=?
a= -9.8m/s^2

so i use the equation V^2=Vinti^2+ax to find the final v
and then use the Vfinal= v initial+at to find the time the ball hits the ground
and use this time to find the avg velocity of the boy running to the building

The Attempt at a Solution

Am i taking the right steps thank you

 

[mgb_phys]

Do you need the final velocity?
You know V_init and distance - you want time
What's the motion equation for distance/time/V_init ?

ps V^2=Vinti^2+2ax by the way.

 

[star20]

Do you need the final velocity?
You know V_init and distance - you want time
What's the motion equation for distance/time/V_init ?

ps V^2=Vinti^2+2ax by the way.

do i use the equa y=vinitial t +.5 at^2

 

[mgb_phys]

Yes, watch the signs of v and a