a paper weight is dropped from the roof a block of multi storey flats. each story is 3m high if it passes the ceiling of the 20th storeys at 30m/s how many storeys does the flat have
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The paper weight was dropped from rest from the roof of the x storey building.
It is given that the weight passes the ceiling of the 20th storey. That means when the weight is momentarily at the ceiling of the 20th storey, 20 storeys of the builiding are below it.
This means that if the building has a total of x storeys then the weight must have passed exactly (x-20) storeys on its way down.
Since the length of each storey is 3m, the total length of (x-20) storeys will be 3×(x-20).
Hence, the paper weight has travelled a distance of 3(x-20) from the top of the building and now reached the ceiling of the 20th storey with a speed of 30m/s.
Here, we can apply the 3rd equation of motion,
v²= u² +2as
v= 30m/s
u=0 m/s
g= 10 m/s²
s = 3(x-20)
30² = 2× 10 × 3(x-20)
15 = x - 20
35 = x
Hence, the builiding has 35 storeys.
I hope you understand the concept.
All the best!
It is given that the weight passes the ceiling of the 20th storey. That means when the weight is momentarily at the ceiling of the 20th storey, 20 storeys of the builiding are below it.
This means that if the building has a total of x storeys then the weight must have passed exactly (x-20) storeys on its way down.
Since the length of each storey is 3m, the total length of (x-20) storeys will be 3×(x-20).
Hence, the paper weight has travelled a distance of 3(x-20) from the top of the building and now reached the ceiling of the 20th storey with a speed of 30m/s.
Here, we can apply the 3rd equation of motion,
v²= u² +2as
v= 30m/s
u=0 m/s
g= 10 m/s²
s = 3(x-20)
30² = 2× 10 × 3(x-20)
15 = x - 20
35 = x
Hence, the builiding has 35 storeys.
I hope you understand the concept.
All the best!
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