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avatar+2390 

The CN tower is 533 meters tall.

 

a) If a heavy rock is dropped from the tower, how long will it take to hit the ground?

 

b) What is its velocity the instant it hits the ground? (Not 0, the instant before it it hits the ground)

 

I wrote up an explanation in this google document on my attempt

https://docs.google.com/document/d/1mi5p3SrO_MEV3VdqbpHTNhaY2UKbWdJR7_oTeO-Lqrs/edit?usp=sharing

 

Apparently one of my classmates said my solution is wrong, and this is his explanation:

so 

Distance:D

Initial velocity is Vi

Final Velocity is Vf

time is T

acceleration is A

and average velocity is Vavg

so

D=Vavg*T

Just the definition of average velocity

D=1/2(Vi+Vf)*t

because 1/2(Vi+Vf) is always average velocity under constant acceleration (It helps to pause and think about it)

D=1/2(Vi+Vi+at)*t

the final velocity is just the change in velocity(a*t) plus the original velocity

D=1/2(2*Vi+at)*t

Combine like terms

D=Vi+1/2*a*t^2

distribute the 1/2

now you plug in the values and solve

10.4295498562537027982 should be the answer

 

Who is right? What is wrong with my method if I am wrong? What is wrong with his method if HE is wrong?

 Oct 17, 2019
edited by CalculatorUser  Oct 17, 2019
 #1
avatar+6045 
+3

....

 Oct 17, 2019
edited by Rom  Oct 17, 2019
edited by Rom  Oct 18, 2019
 #2
avatar+2390 
+2

Oh ok! I will always trust a systems engineer (i think thats what you are if my memory serves me correctly)

CalculatorUser  Oct 17, 2019
 #3
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Aren't these the standard equations of free falling bodies?
Distance d, travelled by an object falling for time t.
d = 1/2 * g * t^2
533 =1/2 * 9.81 * t^2
t =10.424 seconds

Instantaneous velocity v  of a falling object that has travelled distance d :
v =Sqrt(2 * g * d)
v =Sqrt(2 * 9.81 * 533)
v =102.262 m/sec

 Oct 17, 2019
 #4
avatar+2390 
+2

We actually haven't learned these equations

 

we only learned acceleration and velocty formulas.

 

That problem was a challenge because we were supposed to "discover" these equations on our own.

 

im in 8th grade its all new tah meh

CalculatorUser  Oct 17, 2019
edited by CalculatorUser  Oct 17, 2019
 #5
avatar+656 
+1

rip i remember that nasty velocity and acceleration stuff from last year and i did not like it at all 

lol........physics is definitely not my best subject :_ ( 

Nirvana  Oct 17, 2019
 #6
avatar+2390 
+1

I like Physics, only because it has so much to do with math. Except when the teacher gives me a bad grade XD (happening right now I have a solid B+)

CalculatorUser  Oct 18, 2019
 #7
avatar+656 
0

same though

Nirvana  Oct 18, 2019

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