At a building site in Perth, a tower crane is lifting a 300 kg pallet of bricks upwards at a steady speed. The cable from which the bricks are suspended has a circular cross-section of radius 1 cm. What is the tensile stress in this cable?
A)9.4x106 N m-2.
B)9.5x105 N m-2.
C)95 N m-2.
D)936 N m-2.
E)9.4x104 N m-2.

Question

Quizplus · Accepted Answer

To find the tensile stress in the cable, we need to use the formula: 
Stress = Force/Area

The force in this case is the weight of the pallet of bricks, which is 300 kg multiplied by the acceleration due to gravity (9.81 m/s^2) = 2943 N.

The area is the cross-sectional area of the cable, which is a circle with radius 1 cm, so the area is pi times the square of the radius.

Area = pi x (0.01 m)^2 = 3.14 x 10^-4 m^2

Now we can calculate the stress:

Stress = 2943 N / 3.14 x 10^-4 m^2 
= 9.37 x 10^6 N/m^2

Therefore, the tensile stress in the cable is 9.4x10^6 N/m^2, which is answer choice A.

At a Building Site in Perth, a Tower Crane Is