The ratio of the stresses produced by a suddenly applied load and by a gradually applied load on a bar, is A. $$\frac{1}{4}$$ B. $$\frac{1}{2}$$ C. 1 D. 2

The correct answer is $\boxed{\frac{1}{4}}$.

When a load is applied suddenly, the bar has no time to deform and the stress is higher. When a load is applied gradually, the bar has time to deform and the stress is lower.

The ratio of the stresses produced by a suddenly applied load and by a gradually applied load on a bar is called the impact factor. The impact factor is a dimensionless number that is greater than 1. The impact factor depends on the material properties of the bar and the shape of the load.

The following is a brief explanation of each option:

• Option A: $\frac{1}{4}$. This is the correct answer. The impact factor is greater than 1, so the stress produced by a suddenly applied load is greater than the stress produced by a gradually applied load.
• Option B: $\frac{1}{2}$. This is not the correct answer. The impact factor is greater than 1, so the stress produced by a suddenly applied load is greater than the stress produced by a gradually applied load.
• Option C: 1. This is not the correct answer. The impact factor is greater than 1, so the stress produced by a suddenly applied load is greater than the stress produced by a gradually applied load.
• Option D: 2. This is not the correct answer. The impact factor is greater than 1, so the stress produced by a suddenly applied load is greater than the stress produced by a gradually applied load.