## anonymous 3 years ago 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?

1. anonymous

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!!

2. anonymous
3. anonymous

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

4. anonymous

oh you put in the word "dropped" tsk tsk

5. anonymous

I just can't find the corriect value

6. anonymous

sorry that's what the question said

7. anonymous

:P

8. anonymous

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

9. anonymous

yes

10. anonymous

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

11. anonymous

set equal to zero, then put $$t=1$$ to solve for $$v_0$$

12. anonymous

208?

13. anonymous

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

14. anonymous

oh no your answer will have a $$v_0$$ in it

15. anonymous

I plugged in 1 for t and got the 208

16. anonymous

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

17. anonymous

$0=-16+v_0+224$ $v_0=-208$

18. anonymous

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

19. anonymous

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

20. anonymous

yes you did

21. anonymous

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

22. anonymous

yw always good to have another pair of eyes