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?

CalculatorUser Oct 17, 2019

#1

#2**+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**0 **

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**

Guest Oct 17, 2019

#4**+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

#5**+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**+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