Final Velocity Question

[hamid14]

I think I've solved this question correctly, but I am not really sure. My answer was that the final velocity is 5.2 m/s [down]
Also, I used this formula. delta D = V1 * delta T - 1/2 * a * delta T squared

here's the question: The acceleration due to gravity on the moon is 1.6 m/s squared [down]. If a baseball was thrown with an initial velocity of 4.5 m/s [up], what would its velocity be after 4.0s?

[andrew.]

I believe that the answer is 1.9 m/s [down].

Here's how I did it:

[TerranceN]

Because there is constant acceleration,
Vf = Vi + at

Next you need to set a direction as positive, I chose up

Then you can just calculate your answer (remember that acceleration is down so it will be negative)

Vf = 4.5 - 1.6 * 4
Vf = -1.9

Since negative represents down the final answer is 1.9 m/s [down].

Also, what other formula did you use (probably the Vf version of that one?), what you posted would only give you the displacement.

@andrew: beat me by less than a minute, and you even had a fancy picture...

[hamid14]

he didnt give us that formula. thanks

[andrew.]

You can create that formula by using the definition of acceleration:

a = ∆v/∆t (the change in velocity divided by the change in time)

So,
a = (v2 - v1)/∆t

Now rearrange:
a∆t = v2 - v1
a∆t + v1 = v2

v2 = v1 + a∆t