# Instantaneous velocity of a object in projectile motion

1. Nov 13, 2010

### NightRunnerz

1. The problem statement, all variables and given/known data
stone is thrown horizontally with a initial speed of 8.0 m/s (Vxi)
Air resistance is negligible. average acceleration due to gravity = 9.8 N/Kg (down) [ay]

2. Relevant equations
dx= Vxi/ time
Vfy= vyi + ay x time
Instantaneou velocity equation? :S

3. The attempt at a solution
okay so it tells me to find horizontal and vertical components of displacement and instantaneous velocity at time=0.0s/1.0s/2.0s and 3.0s isn't Vyi given (initial y velocity SINCE it's 0?) and (vxi is also give - 8.0 m/s)
BUt how do i find INSTANTANEOUS velocity?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 14, 2010

### tiny-tim

Welcome to PF!

Hi NightRunnerz! Welcome to PF!
Instantaneous velocity just means the velocity at that particular moment (ie, the word "instantaneous" is unnecessary )

(and if you need the speed, use Pythagoras! )

3. Nov 14, 2010

### NightRunnerz

OKAY so by velocity you mean V as in speed right?
dotdotdot m/s2?
.....m/s2?

4. Nov 15, 2010

### tiny-tim

Hi NightRunnerz!

(just got up :zzz: …)
No, speed and velocity are different.

Speed is the magnitude of velocity.

Velocity has components, speed doesn't.

The question tells you to find the horizontal and vertical components of instantaneous velocity … that's vx and vy.
m/s2 is acceleration