Projectile physics problem without the angle given HELP

[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!

 

[Villyer]

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

 

[physics_idiot]

well I know that if the horizontal velocity is 6.0 then 6.0=vi(cosθ), but it doesn't actually give me any other information, and I need to know the vertical velocity in order to solve the problem.

 

[gonzacf]

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.

 

[asteriatic]

Hi there,

I understand that you are struggling with this projectile physics problem without the given angle. Don't worry, we can still solve it without knowing the angle. Here's how:

First, let's define some variables:
- vi = initial velocity (6.0 m/s)
- vf = final velocity (unknown)
- a = acceleration due to gravity (-9.8 m/s^2)
- t = time taken (unknown)
- Δx = displacement (unknown)

We can use the equation vf = vi + at to solve for the final velocity. So, we have:
vf = 6.0 + (-9.8)t

Next, we can use the equation Δx = vit + 1/2at^2 to solve for the displacement. So, we have:
Δx = (6.0)t + 1/2(-9.8)t^2

Now, we know that the displacement is equal to 80 m (the height of the cliff). So, we can set up an equation:
80 = (6.0)t + 1/2(-9.8)t^2

This is a quadratic equation that we can solve for t using the quadratic formula. Once we have the value of t, we can plug it back into the equation for vf to find the final velocity. Then, we can use that final velocity to calculate the distance from the base of the cliff where the keys will land.

I hope this helps! Let me know if you have any further questions. Good luck!