Thanks Woody! I have worked through your comments and have some progress to show. Really appreciate your help.

BUT SOMETHING IS REALLY WRONG - WHAT HAVE I DONE WRONG...please help.

**Question: A safety harness is connected to a cable with a report breaking stress of 800MNm-2.**

What mass could be hung from a harness if the diameter of the cable was 6mm?
We need to use formula Stress = force / area to get the force value. To calculate the area we look to the diameter of cable (6mm), so radius is 3mm. To find area (A) of the cable surface (cross-section) the formula is A = π r2

A = π x 32

= 28.27mm2 (to 2 dp)

=28.27 x103m2 (in SI Units of m)

We also need to convert the stress into SI units

So 800MNm-2 becomes 800 x 106Nm-2

So back to σ = F / A. We know the stress and the area so we need to find force (F). So lets swap the formula around to F = σ A

F = σ A

= 800 x 106Nm-2 x 28.27 x 10-3m2

= 800 x 106Nm-2 x 0.02827m2

= 22,616,000 N

Then to get mass we can use F = ma where F = force, m = m and a = acceleration to rearrange the formula to find mass

M = F

A

= 22,616,000

9.8

= 2,307,755.1kg

But surely this is way too big – where have I gone wrong….help please!