Calculate the stress.
a force of 50 n is acting on an area of 5 mm2.
stress is
mn/m2
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You are given  a force of 50 Newtons and an area of 5 square millimeters. The problem requires you to find the stress in mega Newton per square millimeters. Before anything else, make sure to change the units in its desired form. 50 N is equal to 50*10^-6 mega Newton. The equation of stress is force over area. We have  solution of,  

S = F/A
S = 50*10^-6 MN/5mm2
S = 1*10^-5 MN/mm2
The stress produced for a force of 50N and 5mm2 is 1*10^-5 MN/mm2.

1. C
L=1/2(Pxl)
L=1/2(20x9)
L=1/2(180)
L=90

SA=1/2(Pxl)+B
SA=90+5^2
SA=115

B, A, C, B.