Projectile physics problem without the angle given HELP

AI Thread Summary
To solve the projectile physics problem of throwing car keys horizontally at 6.0 m/s from an 80 m high cliff, first calculate the time it takes for the keys to fall using the vertical motion equations, considering the acceleration due to gravity. The time can be determined from the equation for free fall, which does not require an initial vertical velocity. Once the time is known, use it to find the horizontal distance traveled by multiplying the horizontal speed (6.0 m/s) by the calculated time. This approach effectively separates the vertical and horizontal motions to find the distance from the base of the cliff where the keys will land. Understanding this method is crucial for solving similar projectile motion problems.
physics_idiot
Messages
2
Reaction score
0
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!
 
Physics news on Phys.org


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


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.
 


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.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

projectile motion problem with no initial velocity given
Replies
3
Views
707
Find Projectile Flight Time Given Only Maximum Height
Replies
4
Views
2K
How Does Projectile Angle Affect Asymptotic Behavior in Physics Graphs?
Replies
23
Views
3K
I need opinions on a Projectile Motion problem that I made up
Replies
11
Views
2K
Projectile Angle Calculation: Finding Optimal Launch Angles for Accurate Hits
Replies
3
Views
2K
Find final velocity in a horizontal projectile motion
Replies
2
Views
4K
Projectile Motion -- Help please understanding these basic problems
Replies
4
Views
1K
How Do You Solve for Final Velocities in Elastic Collisions?
Replies
20
Views
2K
Why do I keep getting friction coefficient as a negative?
Replies
17
Views
3K
Relationship between Launch Angle & Horizontal Distance
Replies
15
Views
9K

Hot Threads

Recent Insights

Back
Top