# A-level Physics (Advancing Physics)/Stress, Strain & Young's Modulus/Worked Solutions

1. stress=force/cross-sectional area

```    =100/(0.5x10^-6)m
=200000000Pa
```

2. cross-sectional area=force / stress

```     =100N / 70MPa
=1.428x10^-6
```

3. strain=extension/original length

```     = 2/10
= 0.2
```

4. Decimal --> percentage

```     = 0.2*100
= 20%
```

5. young modulus=stress/strain

```     = (force/area)/(extension/length)
= (force x length)/(area x extension)
= (50 x 0.7)/(0.05 x (pi x 0.001^2)
= 2.23x10^8
```

8. Tensile Strength = Force / Area

```     = 0.95x10^6 = 25/A
= 25 / 0.95x10^6 = A
= A = 2.63x10^-5
```

9. force/area = (young modulus)(extension/length)

```     = extension = ( length x force ) / ( area x young-modulus )
= ( length x force x 4 ) / ( pi x diameter^2 x modulus )
= ( 1E4 * 10 * 4) / ( 3.14159 x 4E-6 x 9E11 )
= 3.54E-2 meters = 3.54 cm
```

10. 10 Newton = mg = (kilograms)x(9.8 m/s/s)

But you have to be careful here because although they say a kilogram "equals" about 2.2 pounds, the pound is a unit of force (not mass). Google replaces "equals" with "means", to obtain:
```    kilograms = (10 / 9.8) = 1.020498
1 kg "means" 2.2046226218 Pounds (from Google)
m "means" 1.020498 kg (2.2046226218 Pounds/kilogram)
10 Newtons "means" 2.25 pounds
Or, just google how many pounds is 10 Newtons to get 2.248 Pounds.  I don't know where I lost the .002 Pounds.  I wouln't have written the question if I knew it was this hard!
```