Normal Stress In A Simple Beam

[Baumer8993]

Homework Statement

In a prismatic bar (same cross sectional area throughout the entire length), the load applied to both ends is 100 N causing the member to be in tension. If the cross sectional area of the member is
5 cm². What is the normal stress in the in kPa?

Homework Equations

stress = force / area

The Attempt at a Solution

I first tried without looking at the units, and got 20, which is wrong. I next tried converting everything to m² to get the answer is pascals the convert to kPa. I got 200 for my second answer. What am I doing wrong? This seems like such a simple problem!

 

[SteamKing]

What are the derived units of a Pascal? Are they N/m^2 or N/cm^2?

 

[Baumer8993]

They are N/m^2. I used an online converter to check, so I confused about what I did wrong.

 

[barryj]

Is the bar supported in the middle? If so, should the force be 100 or 200 N?
How did you get 20?

 

[Nickie]

As a scientist, it is important to carefully consider the units involved in a problem and make sure they are consistent throughout the calculation. In this case, the cross sectional area is given in cm^2 while the load is given in N, so they need to be converted to the same unit before calculating the stress. Converting the area to m^2, we get 0.0005 m^2. Then, using the equation stress = force/area, we get a stress of 200,000 Pa. To convert to kPa, we divide by 1000 and get a final answer of 200 kPa. It is important to pay attention to units in all scientific calculations to ensure accuracy.