Pile Driver Kinetic Energy - alert-apps32’s blog

1. A pile driver falls a distance of 2.50 m before hitting a pile. Find its velocity as it hits the pile. 2. A sky diver jumps out of a plane at a height of 5000 ft.

To illustrate the conversion of gravitational potential energy into kinetic energy and then into work. Equipment. Pile driver shaft, cylindrical iron weight, wood.

What will be the kinetic energy of the ram of a pile driver when it suddenly undergoes a 10-kJ decrease in potential energy.

2 KINETIC AND POTENTIAL ENERGY Potential Energy An object can store energy as the result of its position. For example: the heavy ram of a pile driver is storing.

Hi,

I did some calculations but somehow I feel it s not 100 correct. Could someone have a look please.

Many Thanks

Task

A pile driver of mass mh has struck a pile of mass mp and driven the pile D meters into the ground, if the velocity of the strike is V, determine the force due to the resistance in the ground by the following methods:

1. D Alembers Principle

2. Conservation of energy

V 3.62m/s

mh 100kg

mp 200kg

D 0.08m

g 9.81 m/s 2

SOLUTION:

v 2 u 2 2as

where

v initial velocity

u final velocity

a acceleration

s displacement

transposed the formula to get the acceleration.

Deceleration

a v 2 - u 2 / 2s

a 3.62 2 - 0 / 2 0.08

a -81.9 m/s 2

F ma

F 200 100 81.9

F 24570N

Ground Resistance

R 300 9.81 24570

R 27513N

For the second part I m trying to work out the Potential and Kinetic energy but then i have no idea what to do next.

K.E 1/2 mv 2

K.E 1/2 200 3.62 2

K.E 1310.44J

Height of fall

1/2mv 2 mgh

Transposed to make h the subject

h 1/2 mv 2 / mg

h 300 3.62 2 / 2 200 9.81

h 1m

P.E mgh

P.E 200 9.81 1

P.E 1962J

Since the pile has mass, I am unsure from the problem if the given strike velocity is the same as the initial velocity of the driver-pile system as they start their decent into the ground. If it is, I agree with your solution in the first part for R 27,513 N. To solve using energy methods, remember to include the work done by the ground resistance force delta KE plus delta PE W 0. And check the value you are using for the mass.

That s the conclusion which I came to early today : and it works out now how to delete this post, as there are people on my course that won t do the work just Google it and copy the work that took me 3 days to do.

Thanks for the help.

I guess I can delete my post if you delete yours, but a good teacher or TA or Prof will sort out the cheaters from those who have spent hours of work on the problem. But we don t really have an answer here yet; we ve assumed the strike velocity to be the same as the initial velocity of the driver/pile system, but if the problem defines strike velocity as the speed of the driver head just before impact, then you need to first apply conservation of momentum principles to determine the initial speed of the driver/pile system as if the collision of the two were totally inelastic that is, they join together during impact and proceed downward into the ground as one unit during the 0.08m decent. I think the problem statement is not clear.

I will actually gamble at this stage and stick with the first answer of 27513N i realy hope this is right

I would have assumed that the velocity of the strike was the speed of the pile driver just before it collided with the pile.

I m inclined to agree.

damn it. back to work than

ok I redone my calculations and now the results from the first method don t match the results of the second. Another remark from my side - I don t expect this task to by super duper complex. While if I apply the numbers as assumed at the beginning it all works out with only a difference of 0.27.

You ve done something wrong. In your first attempt, when using the initial velocity of 3.62, you arrived at the same answer for R using Newton s laws versus Energy methods. Now in your new attempt, you need to calculate the initial velocity based on the conservation of momentum principle, then the steps after that to solve for R by either method, are the same. Only V_initial changes.

That does look ok now, If u assume that the velocity given is the velocity before strike : I can always argue the case that the problem was not stated clear enough. But for the first time actually now I feel like this is it.

Still waiting for comments before I delete this post.

Many Thanks

Dark

mementum before impact 100 200 3.62 362Ns

you mean of course 100 3.62 362 N-s

Looks good, so I guess its OK to sound the trumpet, on the assumption that Doc Als assumption, which I agree with, is correct. What sort of a gambler are you.

you mean of course 100 3.62 362 N-sLooks good, so I guess its OK to sound the trumpet, on the assumption that Doc Als assumption, which I agree with, is correct. What sort of a gambler are you.

Thanks for showing me that 100 3.62 362 N-s.

I m the type of gambler that will make one paper for each assumption my initial and Doc Als, handle them in an A4 page with an explanation why there are two papers :

If you deleted your original post, you would only have had one paper to submit, probably the wrong one. Just something to think about.

Demos: 1M-05 Pile Driver. This demonstration illustrates the connection between work and energy. A large mass the pile is raised to a known height.

Are you sure you want to delete this answer.

Sorry, something has gone wrong.

Best Answer:

The decrease in potential energy will lead to the same increase in kinetic energy, so 10kJ more than it started

Source s :

What will be the kinetic energy of a pile driver ram when it undergoes a 10 kJ decrease in potential energy.

Add your answer.