To transport a series of bundles of shingles A to a roof, a contractor uses a motor-driven lift consisting of a horizontal platform BC which rides on rails attached to the sides of a ladder. The lift starts from rest and initially moves with a constant acceleration a(1) as shown. Knowing that the coefficient of static friction between a bundle of shingles and the horizontal platform is 0.25 , determine the largest allowable acceleration a(1) , if the bundle i, NOT to slide on the platform. (Fig 2).

2. A 10 mm diameter cylindrical specimen of an aluminium alloy is loaded in uniaxial tension in a testing machine. a) If the specimen begins to yield at a load of 30 kN, what is the yield stress of the material? b) At the point where yielding begins, the measured increase in length between two points initially 50 mm apart is 0.27 mm. At what strain does yielding occur? c) If the load-deflection curve is linear up to the yield point, what is the elastic modulus of the material? d) If the diameter of the specimen was reduced by 18 um at the yield point, what is the Poisson's ratio of the material? [ans.: (a) 382 MPa; (b) 5.4E-3; (c) 70.7 GPa; (d) 0.333]

A specimen is originally 300 mm long, has a diameter of 14 mm, and is subjected to a force of 2kN. When the force is increased from 2kN to 8kN, the specimen elongates 0.225 mm. Determine the modulus of elasticity for the material if it remains linear elastic. Express the answer to three significant figures and include the appropriate units.

2 m B specimen How did you find the air resistance for the impact test experiment?