Question

A paper weight is dropped from the roof of a block of 35 storey building. Each storey being 3 metre high. It passes the ceiling of the 20th storeys at x m/sec. If g=10m/s2, find x

Answer 1

A paper weight is dropped from the roof of a block of 35 storey building and each storey being 3 metre high.

so height of building, h = 35 × 3 = 105m

the paper weight passes the ceiling of the 20th storey.

so, distance travelled by the paper weight , S = height of building - length of 20 storeys = 105 - 20 × 3 = 45m

initial velocity of paper weight, u = 0

using formula, v² = u² + 2as

given, velocity at 60m , x m/s

so, v = x , u = 0, a = 10m/s² and s = 45m

then, x² = 0 + 2(10)(45) = 900

so, x = 30m/s [Ans]

Answer 2

$\huge\bold\purple{Answer:-}$

u=0, v=30, a=g=10

applying the formula v2-u2=2as ,

s=45m

as each storey being 3m high ,

45/3 = 15 storeys

so, 20 + 15 = 35 storeys