Question

An object is dropped from a tower of height 224 feet, subject to only the constant acceleration of −32 ft/sec2 due to gravity.
(d) What should its initial velocity be in order to strike the ground after 1 second?

Answer 1

clearly the word "dropped" here is inappropriate, since they are asking what hthe initial velocity should be
if it is dropped, the initial velocity is 0!!

Answer 2

http://i50.tinypic.com/34ip8a8.png

Answer 3

In order to reach the ground in 1 second the Vi would have to have a negative velocity of some value otherwise it would not be fast enough

Answer 4

oh you put in the word "dropped" tsk tsk

Answer 5

I just can't find the corriect value

Answer 6

sorry that's what the question said

Answer 7

:P

Answer 8

lets try this
\[a(t)=-32, v(t)=-32t^2+v_0, p(t)=-16t^2+v_0t+224\]

Answer 9

yes

Answer 10

or more commonly written
\[h(t)=-16t^2+v_0t+224\]

Answer 11

set equal to zero, then put \(t=1\) to solve for \(v_0\)

Answer 12

208?

Answer 13

\[t^2-\frac{v_0}{16}-14=0\]

Answer 14

oh no your answer will have a \(v_0\) in it

Answer 15

I plugged in 1 for t and got the 208

Answer 16

oh wait, you are right
put \(t=1\) set equal to 0 solve for \(v_0\)

Answer 17

\[0=-16+v_0+224\]
\[v_0=-208\]

Answer 18

i see the problem
it is negative and you put 208 i bet

Answer 19

Oh! Darn. I even said it have to be negative in the beginning didn't I? X(

Answer 20

yes you did

Answer 21

I plugged it in :) it's right :P thanks! I knew I had to be right but I'm always missing some stupid detail!

Answer 22

yw
always good to have another pair of eyes