# Homework Help: Physics problem I cant get

1. Sep 4, 2004

### ZeroCool

1.5 = (0.25 m/s)t +(0.48m/s2 )t 2

How do I find what t is???

If you know can you please show me how to do this!!!

This question is relating to a Physics problem that my lab group is stump on

My Aim is Atarikid4000, Thanks.

2. Sep 4, 2004

### HallsofIvy

You have 0.48 t2+ 0.25 t- 1.5= 0.

In general, at2+ bt+ c= 0 has solutions
$$t= \frac{-b+\sqrt{b^2-4ac}}{2a}$$ and
$$t= \frac{-b-\sqrt{b^2-4ac}}{2a}$$.

In your problem, a= 0.48, b= 0.25, c= -1.5.

Last edited by a moderator: Sep 4, 2004
3. Sep 4, 2004

### PRodQuanta

I recommend writing a program in your graphing calculator that automatically will solves using the quadratic formula. Saves time.

My \$.02

4. Sep 4, 2004

### ZeroCool

Thanks for the help!!!!

5. Sep 4, 2004

### robphy

One more thing:

You probably already "got most of the physics" when you arrived at that equation (assuming it's correct)! [That's great!] Given your equation, "solving for t" is a math problem... not a physics problem. The only physics is deciding which of the two roots to accept for your answer.

I tell my students to try to distinguish
"problems with physics" (e.g., what is going on?, how do I set up the problem?, am I using the appropriate physical laws and definitions?, how do I interpret my answer?)
from
"problems with math" (e.g., how do I solve for x?, what is the volume of a cylinder?, should I use sin or cos?, what is the x-component of this vector?).
This helps the student (and me) zero-in on where the real problems lie.

(It's a peeve of mine that "physics" is often mistakenly blamed for problems in math.)