# Homework Help: Initial velocity of a projectile

1. Sep 15, 2010

### jpd5184

1. The problem statement, all variables and given/known data

1. A projectile is launched at angle(theta) relative to the horizontal (see the figure below). The
initial height of the projectile above the surface of the table is h, and it hits the table at
distance (delta)x from the launch point. Find the launch speed vi of the projectile.

2. Relevant equations

(delta x)= Vi(initial velocity of x) + (delta t)
(delta y)=Vi(initial velocity of y)(delta t)-0.5g(delta t)^2
yi=yf (initial position equals final position)

3. The attempt at a solution

i think i have to some for some variable in one equation and then plug that into the other equation and solve for Vi(initial velocity)

2. Sep 15, 2010

### katia11

For your first equation, you probably meant
(delta x)= Vi(initial velocity of x) * (delta t)

And for clarification. . .is the initial height the same as the final height? From reading the question it seems like it is launched above the table, and then hits the table.

Remember that Vix= Vi (cos theta)
Viy= Vi (sin theta)

Is that all the info that was given? There doesn't seem to be any numbers. . .unless the answer is not supposed to be numerical. . .

3. Sep 16, 2010

### jpd5184

for clarification there are not supposed to be any numbers, i just have to solve for initial velocity.

a cannon shoots a ball that lands a certain distance from the ground. when the ball is leaving the cannon its at a height of h. find the initial velocity.