Homework Help: Physics

Posted by GS on Thursday, October 4, 2012 at 9:13pm.

a man is 1.8m tall and is standing at the bottom of a 54m tall building, he looks up and sees a brick that has fallen 39m towards him. how much time does he have to get out of the way before the brick hits him?.

Physics - Elena, Friday, October 5, 2012 at 3:12pm
After covering 39 m the velocity of the brick was
v=sqrt(2gH) = sqrt(2•9.8•39) =27.65 m/s.
The brick has to cover the distance 54-39 -2 =13 m.
h =vt+gt²/2
gt²+vt-2H = 0
9.8• t²+27.65•t -26 = 0
t =-27.65 ±sqrt(27.65²+4•9.8•26)/2•9.8 =
= - 27.65±42.23/19.6
t=0.74 s

Answer this Question

Related Questions

physics - A man standing 15.0 ft away from a light pole which is an additional ...
geometry - chung ho is standing on the top of a building that is 135m tall. The ...
Geometry - A man is sitting by a pool. He looks up at an angle of elevation of ...
Math - Mark wanted to measure the height of a nearby building. He placed a ...
CALCULUS - At 3:00 PM a man 144 cm tall casts a shadow 146 cm long. At the same ...
physics - A cement block accidentally falls from rest from the ledge of a 51.7-...
physics - A cement block accidentally falls from rest from the ledge of a 52.0...
physics - A cement block accidentally falls from rest from the ledge of a 52.1-m...
trig - a 6 foot tall man is standing near a tree on level ground .if the man ...
math - A 2 m tall person standing on the ground looks up at an angle of 34.0 o ...

For Further Reading

First Name:
School Subject:
Answer: