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Hi guys,

this is my first post in this forum. I feel lucky to come across a place like this and even more thankful if i can get help on this problem that i've been spending a loooot of time on :(

Oh yea, I have virtually no background in physics (we mostly watched videos in high school) and i'm taking my first semester of physics in community college; it mainly deals with mechanics. so far in the 2 weeks that have passed, i have studied kinematics in one dimension and free fall body problems. i spent almost the whole day doing free fall body problems to gain insight and intuition on how to solve a problem but some of them are just too tough for me!

Well here's the problem.

Problem: "At t = 0, a stone is dropped from the top of a cliff above a lake. Another stone is thrown downward 1.6s later from the same point with an initial speed of 32 m/s. Both stones hit the water at the same instant. Find the height of the cliff."

My strategy was to solve for the first stone's position and velocity at t = 1.6s. (My reasoning is that at t = 1.6, the second stone is still at the origin being thrown.)

Since both stones hit the bottom at the same time, i assumed that the time elapsed from stone 1's fall at position y(t=1.6) to the bottom at y = h (i let displacement be positive downwards) will be the same time it takes for stone 2 to hit the bottom.

so then i let the displacement from stone 1 at t = 1.6s to the bottom equal (h - 12.557).

i then try to use a formula that will let me solve for time. that is going to be

deltaY = vnot(t) + (1/2)(a)(t)^2.

however, when i substitute in the values i know, i get stuck with two unknowns.

here's the paperwork that i have done so far (sorry if its messy, it's a rough draft that i will eventually transcribe neatly into the final hw paper that i will turn in):

i hope to get a decent handle on kinematics and free fall body problems because this week we're starting projectile motion and then a test covering all this the following week. arrrgh!!

thanks a million guys! :)

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# Homework Help: Free fall body problem, stuck with 2 unknowns

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