# Projectiles question: acquiring initial velocity from force+mass

1. May 13, 2010

### rootoftwo

Hello, this may be a rather simple question but it's beginning to irritate me: If I were launching a marble of, say, 10g (0.010 kg) from a marble launcher with a force of 5N (tell me if this is realistic or not) at an angle of 15 degrees then how would I go about finding the initial velocity of the marble?

Please tell me if I was taking to this question in the correct manner:
I first split the force F into it's horizontal and vertical components:
Fx=5*cos15
Fx=4.83
Fy=5*sin15
Fy=1.29

I then found, using F= m * a, the initial horizontal and vertical acceleration:
Ax = 483
Ay = 129

This is the point I was truly having trouble with, finding the initial vertical and horizontal velocities:

To do this, I assumed that since the initial velocity are found at the moment all of the force is transfered to the marble:

Vx = Ax
Vy = Ay

Is this true?

2. May 13, 2010

### kuruman

You are missing a key number which is how long the force acts on the marble. The longer it acts the higher the initial velocity upon launch. That's because acceleration is a=F/m and v = at = Ft/m.