# Physics 212, Quiz #1a: Dec 3, 1997

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Tarzan, Lord of the Jungle, has a femur (thigh-bone) which is 4 cm in diameter and 45 cm long, under normal conditions. One day, to show off to Jane, he lifts Tantor the elephant (mass = 3000 kg) over his head.

Question 1: What is the stress on Tarzan's femur?

```                           Force            (mass of Tantor)*(g)
Answer:  stress = ------------------- =  ----------------------

(3000 kg)*(9.8 m/s^2)         2.94x10^3 N
= ------------------------  =  ----------------
3.14*(0.02 m)*(0.02 m)      1.26x10^(-3) m^2

= 2.34x10^7 N/m^2

```

Under the stress of Tantor's weight, Tarzan's femur compresses to a length of 44.5 cm.

Question 2: What is the strain exhibited by Tarzan's femur?

```                     change in length     45 cm - 44.5 cm      0.5 cm
Answer: strain = -----------------  = ----------------  = ----------
original length          45 cm            45 cm

= 0.011   (no units)

```

Question 3: Calculate Young's modulus for Tarzan's femur.

```
Answer: the formula involving Young's modulus is

stress   =  Young's modulus * strain

Therefore,
stress          2.34x10^7 N/m^2
Young's modulus = ------------  =  -----------------
strain            0.011

= 2.1x10^9 N/m^2
```