Conservation of energy of two thrown stones

AI Thread Summary
Two stones are thrown from a building, one at a 30-degree angle and the other horizontally, both with the same initial speed. The correct answer to their behavior upon hitting the ground is that they strike at different times with different speeds. Energy conservation principles indicate that both stones start with equal kinetic and potential energy, but their trajectories differ due to the angle of launch. The stone thrown at an angle takes longer to reach the ground because it initially moves upward against gravity. Thus, while their final speeds are equal, they do not hit the ground simultaneously.
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Homework Statement



Two stones are thrown with the same initial speed at the same instant from the roof of a building. One stone is thrown at an angle of 30 degree above the horizontal; the other is thrown horizontally.(Neglect air resistance.), which of the following is true:

(a)The stones strike the ground at the same time and with equal speeds.
(b)The stones strike the ground at the same time with different speeds.
(c)The stones strike the ground at different times with equal speeds.
(d)The stones strike the ground at different times with different speeds.


Homework Equations



E=U+K

The Attempt at a Solution



So I guess the answer is c but I can't explain it. Can anyone help me ?
 
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The answer is C, by reasoning. I didn't do any math, and I haven't taken intro-physics yet, but my reasoning is this:

The speed will stay constant, unless altered by another force, which neglecting air resitance, speed is constant.

So when the rock hits the ground, it will be a the same speed as the other rock. So now it can only be A, or C

However, the rocks have a longer arc-distance to travel, and since one rock won't speed up, the rock that is traveling 30 degrees will hit the ground first, followed by the second rock that was thrown horizantal.

So, we know that the rocks can't hit the ground at the same time, if they are traveling at the same speed,

C.

Hayley
 
Energy is conserved since we are ignoring friction.They also start off with the same amount of kinetic and potential energy. Since they both come to rest at ground level then their potential energies are equal at the end. Their kinetic energies at the end are equal so their velocities are equal (since masses didn't change or anything like that).

Energy conservation is a clean way to look at this, but I don't know if you are familiar with this yet though so let me know if what I said was just confusing.
 
I get it. How about the part of different time ?
 
one stone starts off going against gravity (has some velocity going up), it takes some time for the gravitational force to overcome this upward momentum and make the rock start to fall, while the other rock can doesn't have an upward velocity and can start falling vertically right away.

Beyond this explanation we'd have to use calculus and some equations, which I believe were invented because it gets way to hard and ambiguous to describe the stuff in English.
 
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