omnomnom
  • omnomnom
A stone is dropped from the roof of a tall building. A person measures the speed of the stone to be 49 m/sec when it hits the ground. The height of the building is closest to: Select one: a. 24 meters. b. 49 meters. c. 122 meters. d. 245 meters.
Physics
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
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anonymous
  • anonymous
\[mgh = \frac{ 1 }{ 2 }mv ^{2}\]
anonymous
  • anonymous
you can subtract the mass from both sides which shows that everything falls at the same rate
anonymous
  • anonymous
you know what g is

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More answers

omnomnom
  • omnomnom
Gravity?
anonymous
  • anonymous
yes
anonymous
  • anonymous
so if you plug in the velovity and solve for h which is the height
anonymous
  • anonymous
is this for conservation of energy
omnomnom
  • omnomnom
No this is only for the height of the building
anonymous
  • anonymous
The formula I gave you is the conservation of energy
anonymous
  • anonymous
In this case \(g\) is the gravitational acceleration we talked about in the previous problem.
anonymous
  • anonymous
You cannot solve this with kinematics there are too many unknowns
anonymous
  • anonymous
What do you mean you can't solve it with kinematics?
anonymous
  • anonymous
Yeah I guess you could solve for time in the acceleration then plug it in the average velocity.
anonymous
  • anonymous
I was talking about the \(g\) in your formula.
omnomnom
  • omnomnom
??
anonymous
  • anonymous
Though technically speaking, depending on whether they are on the 'energy' part or the 'kinematic' part of the course decides which method they should use.
anonymous
  • anonymous
that is why I was asking
anonymous
  • anonymous
Last question was a 'kinematic' one so maybe it must be kinematics.
anonymous
  • anonymous
acceleration of gravity = velocity final minus velocity inital divided by time.
anonymous
  • anonymous
@omnomnom Have you talked about work or energy in your class yet?
anonymous
  • anonymous
Like potential energy or kinetic energy?
omnomnom
  • omnomnom
No whats work?
anonymous
  • anonymous
It is something you will learn in the future, most likely.
anonymous
  • anonymous
yes solve for time then plug into \[\frac{ d }{ t }=\frac{ v _{f}+v _{i} }{ 2 }\]
anonymous
  • anonymous
conservation is so much easier to solve
omnomnom
  • omnomnom
it confused me though the first equstion
omnomnom
  • omnomnom
equation*
anonymous
  • anonymous
Don't worry about it.
anonymous
  • anonymous
@omnomnom This is a two step problem. First you want to figure out how long it took to fall. Then you want to use that to figure out how far it fell.
omnomnom
  • omnomnom
oh okay so what equation do i use.... is is\[d =Vi( t)+ a \frac{ 1 }{ 2 }(t^2) \]
anonymous
  • anonymous
You can't use that equation until you find time though.
omnomnom
  • omnomnom
Oh yeah >.<
anonymous
  • anonymous
\[a=\frac{ v _{f}-v _{i} }{ t }\]
anonymous
  • anonymous
you know a and both velocities
omnomnom
  • omnomnom
But we need the time :( Cant i just quess the answer?
anonymous
  • anonymous
Yes, \(a\) is the same as last time... \(9.81m/s^2\)
anonymous
  • anonymous
velocity initial is 0
anonymous
  • anonymous
You are not supposed to guess, because there is already a way to find the answer.
omnomnom
  • omnomnom
but...... Whats the way ?
anonymous
  • anonymous
t=49/9.81
omnomnom
  • omnomnom
answer is 5
anonymous
  • anonymous
yes 5 seconds
anonymous
  • anonymous
then plug in the time into your equation and find x
omnomnom
  • omnomnom
oh hold on
omnomnom
  • omnomnom
i got 49 m/s
anonymous
  • anonymous
that is the velocity
omnomnom
  • omnomnom
so we change the equation now?
anonymous
  • anonymous
you want the height of the building
omnomnom
  • omnomnom
yeah
anonymous
  • anonymous
x=1/2t(vfinal-vinital)
omnomnom
  • omnomnom
122.5 meters?
anonymous
  • anonymous
yes
omnomnom
  • omnomnom
thank you :D
anonymous
  • anonymous
do you understand the kinematic equations
omnomnom
  • omnomnom
The first one ? NO the others Yes
anonymous
  • anonymous
http://www.physicsclassroom.com/
anonymous
  • anonymous
this is a helpfull tool
omnomnom
  • omnomnom
oh kay thank you :D

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