# Thread: Basic Physics Formula Uncertainty

1. ## Basic Physics Formula Uncertainty

Hi,
I came across this formula $\displaystyle d=rt-5rt^2$, and when I used it to solve problems, I got ridiculous answers.

I asked others and they suggested $\displaystyle d=rt-5t^2$, but I am not too sure about it.

Can anyone help we clarify how this formula works? Is it the right formula?

Thanks!

-Masoug

2. Originally Posted by masoug
Hi,
I came across this formula $\displaystyle d=rt-5rt^2$, and when I used it to solve problems, I got ridiculous answers.

I asked others and they suggested $\displaystyle d=rt-5t^2$, but I am not too sure about it.

Can anyone help we clarify how this formula works? Is it the right formula?

Thanks!

-Masoug
Please post an example (exact wording) of the sort of question you are trying to solve by using this formula.

(The formula is probably meant to be $\displaystyle s = ut + \frac{1}{2} a t^2$), which will be in your class notes and textbook.)

3. The question was in the context of trajectories, where we have to find the height of a baseball after impact from a bat. The question supplied the first equation and I get really weird answers.
If an object is thrown into the air with an initial upward velocity of r, then its distance above its starting height at t seconds after it was thrown is approximately $\displaystyle d=rt-5rt^2$ meters. Homer Un, the famous baseball player hit a fly ball to the infield with an initial upward velocity of 30 meters per second.
a. What is the height after 2 seconds?
Any suggestions?

Thanks!

-Masoug

4. Originally Posted by masoug
The question was in the context of trajectories, where we have to find the height of a baseball after impact from a bat. The question supplied the first equation and I get really weird answers.

Any suggestions?

Thanks!

-Masoug
This question is now on my list of stupid questions. What book is it from? It's stupid because of the equation it gives.

My advice is to use the formula I gave you in my first post. Substitute u = 30 m/s, a = -10 m/s^2, t = 2 and solve for s.