# Upward and Resultant Velocity

1. Dec 3, 2015

### Oceanspire

• Poster has been reminded to show their Attempt at a Solution
1. You launch a projectile from a wall that is 2 meters in height. It lands on the ground 2 seconds later.

-What is the initial upward velocity of the projectile at the moment of launch?
-What is the initial resultant velocity of the projectile at the moment of launch?

2. Equations given:
- v = at
- d = (1/2)at2
- t2 = d/a

I tried using the last equation to find the acceleration, but I can't seem to figure it out at all.

Last edited by a moderator: Dec 3, 2015
2. Dec 3, 2015

### haruspex

You need to show some attempt, as per the template and guidelines.

3. Dec 3, 2015

### Oceanspire

This is my homework assignment and these are the equations that were given to me to use but I don't know how. I just need help. I don't know where to start.

4. Dec 3, 2015

### haruspex

Presumably the setting is the surface of the Earth, so you don't need to find the acceleration, it is already known.
It doesn't say, but I assume you are only asked to find the vertical velocity. There's not enough information to find any horizontal component.
The second question makes no sense. Is that the exact wording?

5. Dec 3, 2015

### Oceanspire

Yes, except the first question which I'll fix in a second. I forgot to add that I want to find the initial upward velocity

6. Dec 3, 2015

### haruspex

Ok.
For the first question:
The first thing to do is choose your coordinate system. Which do you want to make the positive direction, down or up? (Up is sort of standard, but it's your choice.)
You know the acceleration (which is?)
You know the time.
What is the net change in height (d)?
The equation you quote, d = (1/2)at2, is not general enough. It assumes starting from rest, which is not the case here. Can you quote a more standard 'SUVAT' equation?

The second question still makes no sense. My guess is they meant to ask for the velocity just before hitting the ground.