# h=-9.8t^2-s, solving for t?

• May 25th 2011, 07:03 PM
ijustdontgetit
h=-9.8t^2-s, solving for t?
(I don't know the exact wording of the problem, and I apologize for any vague details.)
A ball is dropped from 11.6 meters. How long does it take in seconds for the ball to fall? It is represented in the equation h=-9.8t^2 - s, where h is the height of ball when it stops falling, t is the time it takes for the ball to fall, and s is the height the ball is dropped.

So s=11.6, correct? It would be h=-9.8t^2-11.6. Wouldn't h=0, as well? How do I solve for t, the time (in seconds) it takes to fall?

There is also a second half to the problem; if the height the ball was dropped was cut in half, would the time it takes to fall be half as well?

If possible, I need help to this literally ASAP. Thank you VERY VERY much!! (:
• May 25th 2011, 07:20 PM
TheEmptySet
Quote:

Originally Posted by ijustdontgetit
(I don't know the exact wording of the problem, and I apologize for any vague details.)
A ball is dropped from 11.6 meters. How long does it take in seconds for the ball to fall? It is represented in the equation h=-9.8t^2 - s, where h is the height of ball when it stops falling, t is the time it takes for the ball to fall, and s is the height the ball is dropped.

So s=11.6, correct? It would be h=-9.8t^2-11.6. Wouldn't h=0, as well? How do I solve for t, the time (in seconds) it takes to fall?

There is also a second half to the problem; if the height the ball was dropped was cut in half, would the time it takes to fall be half as well?

If possible, I need help to this literally ASAP. Thank you VERY VERY much!! (:

My guess is that this is a physics problem.

First you have the kinematic equation incorrect. It should be

$\displaystyle s=s_0+v_0t+\frac{1}{2}at^2$

Where s is the position v is the velocity and a is the acceleration.

From what you have given in the problem the acceleration of the ball is due to gravity only

$\displaystyle a=-g=-9.8 \frac{m}{s^2}$

Since the ball is dropped its initial velocity is zero and its final height is zero also. so we get

$\displaystyle 0=-4.9t^2+11.6$

From here isolate t squared and then take the square root.

for the 2nd part you can just solve again with half of the height to see if its true or not, but before you do that you should try to figure it out based on physical reasoning.
• May 26th 2011, 02:09 AM
Ackbeet
Quote:

Originally Posted by ijustdontgetit
If possible, I need help to this literally ASAP. Thank you VERY VERY much!! (:

Would this question be counting towards a grade?