How long did it take for the box to travel 4.00 meters?

[hatcheezy]

Homework Statement

A box slides along a surface with a positive initial velocity. It the experiences an acceleration of -0.25m/s^2. After traveling 4.00 meters, its velocity is +0.50m/s. How long did it take for the boxto travel the 4.00 meters?

Homework Equations

$$\Delta$$x=volt + 1/2 a t^2 ??

The Attempt at a Solution

4.00m=(.50m/s)t+1/2(.25m/s^2)(t^2)

(.125m/s^2)(t^2)+(.50m/s)(t)-(4.00m)

-(.50) + - $$\sqrt{(.50)^2-4(.125)(-4)/2(.125)}$$

$$\sqrt{2}$$-.50 = .9seconds?

 

[fatra2]

Not from my calculations.

From you problematic, $$v_0$$ is the initial velocity of the box, which is not equal to $$0.5m/s$$

Cheers

 

[Jack21222]

You got the quadratic formula wrong. Everything is over 2a, not just 4ac.

I had to double-check your initial set-up, because you had acceleration as positive, but after a bit of algebra it's correct. I'm not sure if that was by accident or intentional. You didn't show that step, if it was intentional. V-initial isn't given, so you have to solve for V-initial in terms of V-final, a, and t, which happens to be what you got.

 

[hatcheezy]

You got the quadratic formula wrong. Everything is over 2a, not just 4ac.

I had to double-check your initial set-up, because you had acceleration as positive, but after a bit of algebra it's correct. I'm not sure if that was by accident or intentional. You didn't show that step, if it was intentional. V-initial isn't given, so you have to solve for V-initial in terms of V-final, a, and t, which happens to be what you got.

i set it over 2a...im just wondering if i set the previous equation up properly

 

[Jack21222]

i set it over 2a...im just wondering if i set the previous equation up properly

You did, but I suspect it was due to shear luck, because you didn't show how you went from V_o to V_f, and you didn't show how you went from 'a' being negative to 'a' being positive. According to my early-morning algebra, the set-up is right, however.

And no, you didn't set it all over 2a. If you had, you would have gotten the correct answer.