# Calculating Initial Velocity of a Projectile

• jackanese
In summary, it is possible to find the initial velocity of a projectile if you only know the Force applied (47N) to the projectile and the mass (0.04kg) of the projectile (assuming air resistance is negligible). Although the angle it was fired at doesn't matter, the initial velocity will be the same for any angle.
jackanese
is it possible to find the initial velocity of a projectile if you only know the Force applied (47N) to the projectile and the mass (0.04kg) of the projectile (assuming air resistance is negligible).. oh and the angle it was fired at was 30 degrees..

Good ol' Newton again!

(Angle doesn't matter - the initial velocity will be the same for any angle!)

Just use good ol' Newton's second law: force = change in momentum (and initial momentum is zero).

im sorry i am not following
Newtons second law is basically impulse... which is (delta) momentum / time
but i don't have time or velocity...

Yes, you're right

jackanese said:
but i don't have time or velocity...

Yes, you're right. The question says 47 Newtons, so you do need to know the time.

(It must surely be Newton-seconds? - no-one in their right mind would fire a projectile with anything other than an impulse! )

Try it again, assuming that the total force is 47 Newton-seconds!

ok will do

ok so i just ran a few calculations and i came out with a number... not sure if it is correct because my knowledge of physics is pretty limited...

well first i better explain the experiment i am doing (well yeah i guess it is homework and sorry to the mods for putting it in the section but it was never meant to tern into an explanation) .
i was using a spring to fire projectiles and measure the distance and a bunch of other stuff... but i wanted to find the distance i would get if there was no air resistance (so that i could match it against my results)...

anyways what i did was measure the distance the projectile was in contact with the firing pin(this was .14m). i used that in the impulse formula (using the .14m as the displacement, in velocity) and i worked out the time to be .011sec (the time it was in contact with the pin (well actually it was a bolt)).. anyways i used that time and displacement to work out the velocity (.14/.011) which equaled 12.7m/s... now to me that look like the figure i was expecting but i am not sure if the way i got it is correct.

could anyone verify if it is correct or a load of BS..

thanks a lot tiny tim for your help

## What is the formula for calculating initial velocity of a projectile?

The formula for calculating initial velocity of a projectile is: v0 = √(g * h) where v0 is the initial velocity, g is the acceleration due to gravity, and h is the height of the projectile.

## What units should be used for the variables in the formula?

The units for v0 will be in meters per second (m/s), g will be in meters per second squared (m/s^2), and h will be in meters (m). It is important to use consistent units throughout the calculation to ensure accurate results.

## Can the initial velocity of a projectile be negative?

Yes, the initial velocity of a projectile can be negative if it is launched at an angle below the horizontal. This indicates that the projectile is moving downward at the beginning of its trajectory. However, in most cases, the initial velocity is assumed to be positive as the projectile is launched upward.

## How does air resistance affect the initial velocity of a projectile?

Air resistance can decrease the initial velocity of a projectile. As the projectile moves through the air, it experiences air resistance which acts in the opposite direction of its motion. This resistance can slow down the projectile and affect its initial velocity. To account for air resistance, a more complex formula is needed to calculate the initial velocity.

## What other factors can affect the initial velocity of a projectile?

Other factors that can affect the initial velocity of a projectile include the angle at which it is launched, the mass of the projectile, and any external forces acting on the projectile (such as wind or friction). These factors can influence the acceleration and trajectory of the projectile, ultimately affecting its initial velocity.

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