# Homework Help: Intro projectile motion

1. Feb 5, 2012

### kinslow31

1. The problem statement, all variables and given/known data
A bullet is shot straight up into the air. It reaches a maximum height at h = 612 m.

Find an expression for the initial speed of the ball.

Using your previous results find a numeric time for the total flight time, t until the ball reaches the ground.
2. Relevant equations

3. The attempt at a solution

Ok so im assuming at initial speed y is 0 although it seems like Vo would be zero there to but if i do i got Vot=(1/2)gt^2 Vo = (1/2)gt i think thats right for projectile motion, if it is the expression for t is = 2Vo/g because at that time y=yo=0, but now how do i get a numeric value for it i can't figure out Vo, initial velocity, is it just zero? im pretty stuck here

2. Feb 5, 2012

### jamesrc

If the bullet had an initial muzzle velocity of 0 coming out of the gun, how high would it go?

You are given how high the bullet goes and that it is traveling straight up (against gravity). You also need to realize that the bullet's velocity at its highest point is 0. With that information in hand, you need to relate initial and final velocity to acceleration and distance - initial velocity should be your only unknown (which you can solve for).