# Projectile physics problem without the angle given! HELP

1. Nov 6, 2011

### physics_idiot

projectile physics problem without the angle given! HELP!!

You accidentally throw your car keys horizontally at 6.0 m/s from a cliff 80 m high. How far from the base of the cliff should you look for the keys?

Okay so I honestly don't know how to figure this problem out, but I think that I need to use the equations vf=vi+at and Δx=vit

For the second equation, I know that Δx=(6.0)t. I also know that for the first equation I gave, vf=vi+(-9.8)t. I don't know how to figure it out because I feel like I need the angle in order to find out the rest of the information.

I know it sounds like I am a complete slacker, but I really need help with this as soon as possible! Please help me! Thanks!!

2. Nov 6, 2011

### Villyer

Re: projectile physics problem without the angle given! HELP!!

The angle is given, it is just given indirectly. Reread the first statement.

3. Nov 6, 2011

### physics_idiot

Re: projectile physics problem without the angle given! HELP!!

well I know that if the horizontal velocity is 6.0 then 6.0=vi(cosθ), but it doesnt actually give me any other information, and I need to know the vertical velocity in order to solve the problem.

4. Nov 6, 2011

### gonzacf

Re: projectile physics problem without the angle given! HELP!!

Hi,
Just saw your post and though I guess the answer may come a bit late here it is anyway:

You need to work separately the two relevant coordinates (vertical and horizontal).

Calculate the time the keys will take to fall the 80m of the cliff (vertical acceleration of g (due to gravity) with zero initial velocity.

Once you have this time you work the horizontal direction: a constant speed of 6m/s times the time calculated on the previous calculation.

Hope it helps.