How to Simulate a 15lb Wood 2x4 Impact at 67 mph?

[Moose720]

I posted earlier about testing a project to simulate a wood 2x4 traveling at 67 mph, I did not really get the answers I was looking for so I am going to try to rephase it. My project needs to withstand the impact of a 15lb wood 2x4 traveling at 67 mph. I want to simulate this test but in a vertical fashion. I can set up a drop test up to the height of 15ft. My main question is, how much weight needs to be added to the 15lb wood 2x4 to achieve the same impact as the 15lb 2x4 @ 67mph, and also what height would it needed to be dropped from. Air resistance not a concern for this test. What formulas are used to get the results?

 

[Moose720]

When I say impact, I mean just before the 2x4 would strike the surface.

 

[Moose720]

Or am I looking for Kinetic Energy??

 

[zts1986]

Moose, this is how I would go about it:

1. Figure out how fast the object is moving when dropped from 15 feet. This can be done with the known acceleration due to gravity (32.2 ft/s^2). This is the average acceleration across the Earth's surface. If you wanted a more accurate number, you'd have to factor in your elevation. This won't be necessary or matter for this purpose, unless you're at the summit of Mt. Everest or something. Anyway, the formula for the velocity of a free-falling object on Earth given a certain height is as follows:
v = sqrt(2*g*d)
v = sqrt (2 * 32.2 ft/s^2 * 15 ft)
v = 31.08 ft/s = 21.19 mph

2. Given the velocity of the object in your experiment, the desired velocity, and the desired weight, you can set up an equation of momentum. The main principle here is that you desire a momentum produced by a 15 lb object going 67 mph. Momentum is equal to the product of mass and velocity (p = m*v). Since you're looking to recreate the momentum from the desired experiment and you cannot change the velocity, you have to add mass. That gives you the following equation:
m1v1 = m2v2
(15 lb)*(67 mph) = (X lb)*(21.19 mph)
X = 47.43 lbs

3. So, for your experiment to produce the required momentum, your total weight needs to be 47.43 ~ 47.5 pounds. You currently have a 15 lb mass so therefore, you need to add an extra 32.5 lbs of mass to your weight.

4. Just as a note, there are some inaccuracies in this experiment. The calculations I made were using point-masses, not actual objects. The difference is not very large at all and will be negligable in what you're trying to accomplish. I would not worry about those. I figure that if air resistance isn't necessary, then it isn't necessary to dive into the center of mass/inertia values for the mass.

Hope this helps!

 

[PJC01]

Thank you for sharing your project with us. Impact testing simulation is an important tool in understanding how materials and structures respond to high-speed impacts. In order to accurately simulate the impact of a 15lb wood 2x4 traveling at 67 mph, there are a few factors that need to be considered.

Firstly, the weight and velocity of the impactor (in this case, the 15lb wood 2x4) are important parameters for determining the kinetic energy of the impact. This can be calculated using the formula KE = 1/2 * m * v^2, where KE is the kinetic energy, m is the mass, and v is the velocity of the impactor.

Next, the height from which the impactor is dropped also plays a crucial role. The higher the drop height, the greater the potential energy of the impactor, which also contributes to the overall impact force. This can be calculated using the formula PE = m * g * h, where PE is the potential energy, m is the mass, g is the acceleration due to gravity (9.8 m/s^2), and h is the height.

In order to achieve the same impact as a 15lb wood 2x4 traveling at 67 mph, you would need to determine the combination of weight and drop height that would result in a similar kinetic energy and potential energy. This can be done using the equations mentioned above, along with some trial and error.

It is also important to note that in order to accurately simulate the impact, the material properties of the 2x4 and the surface on which it is impacting should be taken into consideration. This can be done by using impact testing equipment such as a drop tower or a pendulum impact tester.

I hope this information helps you in your project. Best of luck with your impact testing simulation.