niki Posts: 1, Reputation: 1 New Member #1 Nov 20, 2003, 01:19 AM
Problem dilemma
I need help with these problems

1. a 1kg brick fall off a 3m wall onto a man's foot. How long does the brick take to fall. What is the Kenetic Energy of the brick relative to his foot.
 MathMaven53 Posts: 20, Reputation: 2 New Member #2 Jan 8, 2004, 10:51 AM
Re: Problem dilemma
It's been years since I have studied Physics but I'll
work with the equations and you can substitute values into them.

Let s be distance brick falls,m the mass of the brick, g be acceleration due to gravity, t be time of fall, v be velocity of brick.

s = (1/2)g t^2

Solve for t

t = sqrt((2s)/g)

v = gt

= sqrt(2 g s)

Kinetic Energy is given by

(1/2) m v^2

= m g s

g is 32 ft/sec^2 in English system of measurement
but you are using metric. I forget what g is in the
metric system but it should be listed in your physics
textbook.

In summary: To find the time it takes for the brick to fall, use the equation

t = sqrt((2s)/g)

The brick's Kinetic Energy is given by m g s
 Polokid16 Posts: 11, Reputation: -1 New Member #3 Dec 8, 2007, 09:28 PM
Using SI (or english system)

"_" - subscript

E_p = mgh = (1kg)(9.8m/s^2)(3m) = 29.4J

For the time:

d = v_i * t +(0.5)at^2

since v_i or v_initial = 0m/s

d = (0.5)at^2

rearrange to solve for t:

sqrt( d / (0.5)g) = sqrt( 3m / (0.5)(9.8m/s^2)) = 0.6s
 itsme_vipsdude Posts: 29, Reputation: 0 New Member #4 Dec 15, 2007, 03:26 AM
look as the body falls from rest therefore its initial kinetic energy is zero... therefore it must hve only the potential energy... potential energy
=mgh
=30*9.8*1
=294J
thus t the lowermost point kinetic energy is equal to the potential energy lost... tus k.e=294J
 Polokid16 Posts: 11, Reputation: -1 New Member #5 Dec 15, 2007, 06:20 AM
The wall is 3m... but yes E_k = E_p

 Question Tools Search this Question Search this Question: Advanced Search

## Check out some similar questions!

Another trailer dilemma [ 9 Answers ]

I noticed another post on this board about not getting what they paid for! I have much of the same problem with the same trailer manufacturer(Haulmark)! Except I took delivery of the trailer with the exception that I did not sign off on its quality, shortages, damages and let them know the...

Dilemma! (Job in archives) [ 2 Answers ]

I am soon to become a history graduate and had decided that I would like to work in museums/archives. I had therefore decided the best way forward was to do a MA in Museum Studies to which I have been accepted. However, recently I have been told about a job with a local archive center which is a 2...

Switch Dilemma [ 1 Answers ]

I have a switch box that has 1. a white wire that appears to go through from top to bottom; 2. a red wire that come from the top and ends; 3. a red wire that exits at the bottom; and 4. a blue wire that exits at the bottom I am wiring two switches after replacing one, and...

Valentine's Dilemma... [ 1 Answers ]

Are gift cards too impersonal?? My boyfriend and I have been dating for two months. Valentine's is in two days. I'm seventeen, but he's my first boyfriend and I'm completely lost on what to get him. I've never shopped for a boy before! *panics* So basically, what I'm wondering is... ...