Calculating size of rectangle cross section

[rad10k]

Homework Statement

A cmedium carbon steel rod has a rectangular cross section and must cope with a tension of 29 430 Newtons . The thickness of the rod is 15 mm calculate the siz of the cross section?

Homework Equations

A=P/Ok


3. The Attempt at a Solution [/b

O = UTS = 750 Mpa k = 0.25 P = 29 430 N t = 15 mm

A= P/Ok

29 430 / 200 = 187.50 mm^2

187.5 / t = 187.5 / 15 = 12.5 sqrt = 3.5355

Size of cross section = 12.5 mm x 3.5 mm

I believe I have the area correct but not sure if the sides are correct ?

 

[nvn]

rad10k: Your answer is currently incorrect. Check your math. MPa should be spelled MPa, not Mpa. The name Newton is the name of a man, whereas Newton (N) is a unit of force. Also, place a comma between separate equations on the same line, for clarity. Try again.

 

[rad10k]

ok thanks

A=P/Ok

750 * 0.25 = 187.5, 29 430 / 187.5 = 156.96

Area = 156.96 mm^2 from this;

A/t sqrt = 156.96 / 15 = 10.464, sqrt = 3.2348

size of cross sectional area is 10.4 mm x 3.2 mm

 

[nvn]

rad10k: You should not perform sqrt.

 

[rad10k]

so the cross section is 15 mm x 10.4 mm ?

 

[nvn]

rad10k: Your answer is almost correct. Generally always maintain at least four significant digits throughout all your intermediate calculations, then round only the final answer to three significant digits, unless the first significant digit of the final answer is 1, in which case round the final answer to four significant digits.

Even if you round the final answer to three significant digits, you currently rounded it wrong.