# Help with trajectory(Finding initial velocity)

1. Sep 29, 2011

### DeltaZX

I'm trying to help a friend with a physics problem. I've been helping her figure a few out(I always make sure she solves them and understands how she did) but we've hit one thats gotten us both stumped, so I'd appreciate a bit of assistance.

The problem is basically, a Diver dives off a diving board so many meters above the water and hits the water at a certain angle and velocity, using this information we're supposed to figure out the initial velocity and angle. I didn't include the actual numbers because: 1- I dont recall them off the top of my head, and 2- I just want some help getting going in the right direction with this.

Where should I start?

2. Sep 30, 2011

### DiracRules

I can either help you find the solution or write down it.
Now I'll try doing the former but if you want I can tell you the solution.

You can try either to deduce both the components of the velocity, or to calculate separately its magnitude and its direction. I'll do the latter since it is simpler.

1) You can calculate the magnitude of the initial velocity from energetic consideration.

To get the direction:
2) What kind of motion is it? Did you split it into its components?
3) Write down the expression of the velocity (its components, actually) vx=f(t), vy=g(t).
If you did it right (and if I explained you clearly :D) you should see the final steps.

Actually, it's simpler that it seems. The thing is, calculate |v| from energetic consideration rather than from the equations of motion.

I hope I was clear :D