Help with free-fall physics question?

Question

Can I get some help with the work process for this problem?

A cement block falls from a building that's 53 m. When the block is 14 m from the ground, a man, 2 m tall, sees it. How much time does the man have to get out of the way?

Answer 1

Using the movement equation:

y= yo + Vot +1/2 a t²
So, the free fall:
Vo =0 a= g = - 9.81 m/s² and y = -y
Then
y = 1/2 gt² Solving for t:

t = √(2y/g)

Just at the distance where the block will hit the head of the man will be 53-2 = 51m = y

Then the time that the man needs to get out of the way is

t = √[2(51) /9.81] = 3.22 s <<<<<<<<<<<

Answer 2

This is a two part question. How long does it take for the block to fall from 53 m to 14 m, then how long does it take for the block to fall from 53 m to 2 m?
Using the Newtonian formula h=1/2 g t squared. (see http://www.krysstal.com/formulas.html)
Astually we want the formula to read t= square root of distance travelled times 2 divided by 9.81.
Doing this gives t=sqr ((53-14)*2)/9.81=2.82 sec
Then t=sqr((53-2)*2)/9.81=3.22 sec

The acceleration due to gravity is assumed to be 9.81 m/sec squared.

The difference is 3.22-2.82 or about ..404 seconds.

Since human reaction time is typically .75 second, the man is hit!

Sorry about that!

Answer 3

At 14 m from the ground.that means the block would have fallen through 53-14-39 m
velocity then will be=2gh=2*9.8*39
with this initial velocity,the time taken to fall tyhrough 12 m wiilbe
12=2*9.8*39t+1/2*9.8*t^2
=>9.8t^2+4*9.8t-24=0 this will be the equation
solve it for t and you get an idea of how much time the man has tosave himself
(9.8t-4) (t+6)=0 and so t=4/9.8 sec

Answer 4

Time A = 0, release of block
Time B, block at 14 m from ground
Time C, block at 2 m from ground
You wish to know (Time C) - (Time B)

First calculate the speed at Time B, then find Time B. Use the same type of calculations to find the speed at Time B and the Time C.

Answer 5

lol, It doesn´t say if the man is standig upright or not. Also est. the time of reaction, wich is nearly impossible. I would say that the q. is incomplete. Well good luck anyway.