What is the concept of the discount rate primarily used for in engineering economics?

The concept of the discount rate is primarily used to compute present and future values in engineering economics. The discount rate reflects the time value of money, which recognizes that money available today is worth more than the same amount in the future due to its potential earning capacity. This time value is critical for comparing cash flows that occur at different times.

By applying the discount rate, one can determine how much future cash flows are worth in today's terms (present value), or conversely, how much a certain amount today will grow to in the future (future value). Therefore, the discount rate acts as a tool to adjust cash flows to their respective present or future values, allowing for effective decision-making related to investments, project evaluations, and financial planning.

While the other choices (measuring project lifecycles, determining rates of return on investment, and assessing risk management) are important components of engineering economics, they are not the primary role of the discount rate. The discount rate specifically addresses the valuation of cash flows over time, making option C the most accurate representation of its primary use.