Problem Sheet 2

The numbers in square brackets refer to the number of the problem in your textbook.

1. [E4.2] The cable of a hoist has a cross-section of 80 mm2. The hoist is used to lift a crate weighing 500 kg. What is the stress in the cable? The free length of the cable is 3m. How much will it extend if it is made of steel (modulus 200 GPa)? How much if it is made of polypropylene, PP (modulus 1.2 GPa)?
2. [E4.3] Water has a density of 1000 kg/m3. What is the hydrostatic pressure at a depth of 100 m?
3. [E4.4] A catapult has two rubber arms, with a square cross-section with a width 4mm and length 300 mm. In use its arms are stretched three times their terminal length before release. Assume the modulus of rubber is 10-3 GPa and that it does not cahnge when the rubber is stretched. How much energy is stored in the catapult just before release?
4. [E4.8] The stiffness S of an atomic bond in a particular material is 50 N/m and its center-to-center atom spacing is 0.3 nm. What, approximately, is its elastic modulus?
5. [E4.11] If the modulus of the polypropylene is 1.5 GPa, estimate the modulus of a PP foam with a relative density {\tilde{\rho}}/\rho_s of 0.2.
page revision: 3, last edited: 06 Feb 2009 05:45