Originally Posted by **studiot** You are doing the arithmetic the hard way.
But I think you method seems basically sound, unless you have miseed out some information, the 50m rope length is irrelevent.
Youngs modulus = stress/strain
So 64 x 10^7 = stress/strain (note I have got rid of the decimals)
64 x 10^7 21 x 10^-3 = stress in Pascal. = 64 x 21 x 10^4
Force = stress x cross sectional area
F = 64 x 21 x 10^4 x pi x D^2 /4
F = 64 x 21 x 10^4 x pi x 3/2 x3/2 x 10^-2 x 10^-2 /4
= 4 x 21 x pi x 9
See you can almost do it in your head. |

Hi! Thank you for your reply. That is the correct answer!!

Although I have to say I don't know how those numbers work. I am confused where the pi x D^2 /4 comes in, and the 3/2s? And divide it by 4?

If it is stress x cross sectional area, why isn't it just the stress in pascal x cross sectional area:

13440000 x 2pix7.5x10^4

but this = 633345N so obviously that's no good haha.

How would you go about getting those other numbers for the 2400N, if you don't mind me asking? Furthermore, how did the above numbers get simplified for 9 in the final line?

Again, thank you for your comment