# Homework Help: Determining Velocity with Projectile Motion

1. Oct 31, 2007

### TexasCow

1. The problem statement, all variables and given/known data
Ok Im having slight trouble with a homework problem. An arrow was launched at an angle, and hit a balloon that was 150m away and 100m up. I used my distance equations along with initial velocity to calculate the two angles that can be used to hit the balloon, but I'm stuck on the next part. I used t=dx/vx to solve for time, and now I need to solve for the velocity when the arrow hits the balloon. I'm sure it's a simple problem but I'm stuck!

Initial Velocity=60m/s
Distance from 0=150m
Height in Y direction=100m

dy=Voy(t)-4.9t^2

Vx=Vcos(x)
Vy=Vsin(x)

t=dx/vx

I used the four equations above to solve for the angle(s). Then put in the velocities to solve for time. How do I solve for velocity when the arrow hits the balloon?

2. Oct 31, 2007

### saket

You know vertical displacement, you can calculate Vy. Vx will remain constant.

3. Nov 1, 2007

### TexasCow

Should I use Vy=Voy+at?

4. Nov 1, 2007

### HallsofIvy

Yes, if you know V0y and t, you can use that to solve for Vy. You already know that Vx= V0x.

5. Nov 1, 2007

### TexasCow

Yes, I know that Vx is constant throughout the motion. So using Vy=Voy+at, I can solve for the velocity at any one point in time at a certain height?

6. Nov 1, 2007

### saket

You are given height, acceleration due to gravity, and initial Vy. Think of some other s-u-v-a-t formula which could give you final Vy at a given height more quickly!

P.S.:
1. You will get two Vy at a particular heght.. I hope you can decide which one to take!
2. From Vy thus obtained and Vx, you can, of course, obtain final velocity.