# You have with you (1) a string of 1 meter length (2) 1 Kg weight (3) a watch. Now you want to find out the height of the Tallest tower -- say cn tower of toronto. How many ways can you devise to Measure it? They do not have to be practical, but scientifically Correct. Up to seven methods are child’s play.

This question is related to Infosys Interview

#### Bharathy

• Jun 2nd, 2005

1.Go to the top of the building.Attach a weight at the end of the string. Hang it till it touches the ground. Then measure the string.
2.Measure the length of the shadow of the string and shadow of the tower.
len of string:len of srting shadow = len of tower:len of shadow of tower

#### Prasath N

• Jun 10th, 2005

Calculate the time taken for the weight to fall from a height of 1metre.Then calculate the time taken for the weight to fall from the buiding top.Compare both and find the height of the building.

• Jun 23rd, 2005

calculate the number of stairs to be climbed to make it equvalent to 1 mtr of vertical height, note down the time taken to climb these stairs (say t sec) and then the time taken to climb to the top of the stairs (say T sec) maintaining a uniform speed throughout. then the height of the tower will be (T/ t) mtrs.

• Jun 28th, 2005

Since the answer needs to be just scientifically correct and not practically, i guess u can find the height of the tower by measureing it 1 mt a time using the string !!!!!! :)

#### Rajesh

• Jun 28th, 2005

1. Go to the top and drop the 1kg wt. Cal the time taken by it to reach the ground (say t seconds). Den the height is 9.8=h/t*t.

• Jun 28th, 2005

Since the answer needs to be just scientifically correct and not practically, i guess u can find the height of the tower by measureing it 1 mt a time using the string !!!!!! :)

• Jun 28th, 2005

The first answer out of the 2 Posted by Bharathy (on 2005-06-02 09:15:45) can only be true if the tower is less than or equal 1 mt in height, which definately does not qualify it to be a "TALL / TALLEST" tower !!! :)

#### indu

• Jul 8th, 2005

giv the 3 things to the owner of the building and ask him to tell the height.

#### siva

• Jul 16th, 2005

Remove the tower from it's base/root make it fall asleep in horizontal direction and measure it with the help of 1 mtr string

#### siva

• Jul 16th, 2005

Remove the tower from it's base/root make it fall asleep in horizontal direction and measure it with the help of 1 mtr string

#### vikas aggarwal

• Aug 6th, 2005

Just drop the watch from the top and note down the time in which the watch touches the bottom of the tower.
and now apply the formula
h=ut + 0.5gt2

#### Murali

• Aug 27th, 2005

1. Find the time period of osscilation at the top of the tower (making minor correction to center of gravity of 1 kg wt) and the ht of the tower can be calculated. Of the I dont remeber the formula, and too lazy to derive it now...

2. Drop the weight(or watch) ask some one to measure end velocity. u can find the height.
h = v2/2g

#### rajani

• Jun 24th, 2006

hi,

hold the string vertically,drop the weight ,note down the time,now drop the weight fr the tower and calculate in this way  .

1mt->t1

?->t2      (t1,t2 can be known fr watch)

#### natter

• Nov 9th, 2006

just jump from the tower, u will never know what happens next

#### RAGHAVA_KLCE Profile Answers by RAGHAVA_KLCE

• May 11th, 2008

Tie the 1 Kg weight to the 1 meter string at the top of the building.
swing the weight tied.
calculate the time taken to complete one oscillation(this can be done by taking time period for 20 oscillations and divide it by 20 for accuracy).
using the formulae in SHM
g=4*pi^2*L/T^2.
where  L--> length of string
T-->time perio for oscillations
now untie the weight.
leave it down simply and calculate time taken by it to reach down.
now from formula   S=0.5*g*t^2
for 'g' substitute the one calculated from SHM formula.
ofcourse we know g=9.81m/s2, it alters with height and the concentration of buildings sorrounding etc.,hence we calculate g from SHM
calculate height of tower.

#### bhanupratap56 Profile Answers by bhanupratap56

• May 18th, 2008

TIE THE 1KG WEIGHT TO THE 1m string.
1)go to the top of the building make the weight to oscillate and note the time period t1.
2)now repat the same at the bottom of the building and note the time period t2.
we have time period t=2*pie*(l/g)^.5
here l=1m.
therefore g proportional to t^-2.
so  g2/g1=(t1/t2) ^-2-------->eq(1)
g1=G*m1*m2/r^2  r= dist from centre of the earth.
g2=G*m1*m2/(r+h)^2  h= height of the biulding.
on solving we get g2=g1*(1-2h/r).------eq(2)
hence 4m eq 1&2
we get     (t1/t2) ^-2=(1-2h/r).
thus we can get the height of the biulding..

#### abhay_bksc Profile Answers by abhay_bksc

• Jun 16th, 2008

1.Measure with help of String.2.Drop the stone from top of tower and note time taken to fall on ground.Since initial velocity of weight is 0 so put value on h=ut + (1/2)g(t^2) where u=0 so h=(1/2)g*(t^2)3.drop the weight from tower and as it touches ground all potential energy is converted to kinetic energy. so mgh=(1/2)g*(t^2).4. Draw a point on the ground and determine the distance between point and foot of the tower using string.Find angle of elevation or and using trigonometry determine the height of the tower.5.impractical but scientifically correct:-Determine your uniform speed with the help of string and watch. Start walking on the tower with uniform speed and find the finishing time. Then height= speed * time.

#### logu122 Profile Answers by logu122

• Jun 26th, 2008

go to the top of the tower drop 1 kg weight from there, calculate the time taken by the weight to reach the ground....,
then we can calculate the height by using

s=ut+(1/2)at^2.
where is S is the distance travel ie height of the tower,
u is the initial velocity ie u=0,
t is the time taken by the object to reach the ground,
a is the accelaration due to gravity ie a=9.8.

#### piyus kumar Profile Answers by piyus kumar

• Jul 27th, 2008

Attach the 1 kg weight to the string and calculate its time period by the help of watch now using the formula T=2*pi*(l/g)^(1/2) calculate the value of g(say g1) same thing we can do after reaching the top of the tower(say g2) now using (g2/g1)=(1-(2h/R))
where R=6400km,we get h which is height of the tower.

#### sreedhar_28 Profile Answers by sreedhar_28

• Oct 13th, 2008

To find the height scientifically,

s=ut+.5at^2
u=0, t=time taken by the weight from building top to bottom in sec. use watch and find t
a=9.8m/s^2
s=4.9*t^2 m  