How High Was the Stone When It Started Falling?

[joe215]

Homework Statement

A falling stone takes 0.28s to travel past a window 2.2m tall. From what height above the top of the window did the stone fall?

The Attempt at a Solution

Vo=?, the velocity at the top of the window
a= -9.8m/s^2
t=.28s
d=2.2m
v=?

Vo=(1/2at^2-d)/-t

[1/2(-9.8)(.28)^2-2.2]/-.28=9.2m/s

Vo now becomes V although it still represents the velocity at the top of the window.

t=?
d=?
a=9.8 m/s^2
Vo=0
V=9.2m/s

Solve for "D"

D=(V^2-Vo^2)/2a

(9.2^2 - 0)/ (2*-9.8)= -4.3m

The ball is dropped from 4.3m.

Am I right?

Thanks,

Joe

 

[alphysicist]

Hi joe215,

Homework Statement

A falling stone takes 0.28s to travel past a window 2.2m tall. From what height above the top of the window did the stone fall?

The Attempt at a Solution

Vo=?, the velocity at the top of the window
a= -9.8m/s^2
t=.28s
d=2.2m
v=?

Vo=(1/2at^2-d)/-t

[1/2(-9.8)(.28)^2-2.2]/-.28=9.2m/s

This value cannot be right; the object is moving downwards so the velocity must be negative.

The equation before this last one is right, but when you plugged in the numbers you made an error. Do you see what it is?

 

[joe215]

I don't see the error?

 

[alphysicist]

I don't see the error?

d is the displacement; since the stone is falling downwards, d is equal to -2.2m.