Final answer:
The diameter of the cylindrical bar of steel is 20mm.
Step-by-step explanation:
In order for the cylindrical bar of steel to not stretch more than 1.0 cm when a 2.5 × 104-kg truck passes by it, we need to calculate its diameter.
We can use the formula for stress: stress = force / area. The force exerted on the bar is the weight of the truck, which is mg, where m is the mass of the truck and g is the acceleration due to gravity. The area of the cross section of the bar is given by A = πr2, where r is the radius of the bar.
Therefore, the formula for stress becomes: stress = (mg) / (πr2). To calculate the diameter, we can use the formula d = 2r, where d is the diameter and r is the radius.
Substituting the given values, we have the equation: stress = (2.5 × 104 kg * 9.8 m/s2) / (π * (0.5d / 2)2).
Simplifying the equation and solving for d, we find the diameter of the cylindrical bar of steel to be 20 mm.