A stone is dropped from the top of the building and at the same time a 2nd stone is thrown vertically upward from the bottom of the building with the speed of 20m/s.They pass each other 3s later.What is the height of the building?

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Answer 1 · 2018-04-07T06:57:04

The height of the building is #=60m#

Let #h= " height of the building"#

The acceleration due to gravity is #g=9.8ms^-2#

The distance travelled by the stone from the top of the building is #=lm#

The distance travelled by the stone from the top of the building is #=(h-l)m#

Apply the equation of motion,

#s=ut+1/2at^2#

The time is #t=3s#

For the stone thrown from the top of the building

#l=0xx3+1/2xx9.8xx3^2=44.1m#

For the stone thrown from the bottom of the building

#h-l=20xx3-1/2xx9.8xx3^2=60-44.1m=15.9m#

Therefore,

the height of the building is #h=15.9+44.1=60m#