### Correct Option: D. The car would gain infinite mass. #### Detailed Explanation: To understand why option D is correct, we need to delve into the principles of Einstein's theory of relativity, particularly special relativity, which deals with objects moving at high speeds, especially those approaching the speed of light (denoted as \( c \)). 1. **Mass and Speed Relationship**: - According to special relativity, as an object moves faster and approaches the speed of light, its relativistic mass increases. The formula for relativistic mass \( m \) is given by: \[ m = \frac{m_0}{\sqrt{1 - \frac{v^2}{c^2}}} \] where \( m_0 \) is the rest mass, \( v \) is the velocity of the object, and \( c \) is the speed of light. - As \( v \) approaches \( c \), the denominator approaches zero, which means that \( m \) approaches infinity. This implies that it would require an infinite amount of energy to accelerate an object with mass to the speed of light. 2. **Implications of Infinite Mass**: - If a car were to somehow exceed the speed of light, it would theoretically possess infinite mass. This is not just a mathematical abstraction; it suggests that the laws of physics as we understand them would break down. The energy required to maintain such a speed would be beyond any conceivable limit. 3. **Why Other Options Are Incorrect**: - **A. The car would create a visible sonic boom.** - A sonic boom occurs when an object travels faster than the speed of sound in a medium (like air). However, the speed of light is not analogous to the speed of sound. The effects of traveling faster than light are not well-defined in our current understanding of physics, and thus, this option is misleading. The concept of a sonic boom does not apply to light-speed travel. - **B. Time would slow down for the passengers inside the car.** - This statement is partially true but misapplied in this context. According to relativity, as an object approaches the speed of light, time dilation occurs, meaning time would slow down for the passengers relative to an outside observer. However, if the car were to exceed the speed of light, the concept of time dilation becomes undefined, and thus this option does not accurately describe the scenario. - **C. The car would appear to be in two places at once.** - This option is a misinterpretation of relativistic effects. While there are phenomena in quantum mechanics that can lead to particles being in superpositions, in the context of relativity and macroscopic objects like cars, this does not apply. An object cannot be in two places at once simply because it exceeds the speed of light; rather, it would violate causality and the fundamental laws of physics. #### Summary of Key Points: - As an object approaches the speed of light, its relativistic mass increases, theoretically becoming infinite at light speed. - Exceeding the speed of light is not supported by current physics and leads to undefined scenarios. - Sonic booms are related to sound, not light, making option A incorrect. - Time dilation applies only as speeds approach light, not beyond it, making option B misleading. - The idea of being in two places at once does not apply to macroscopic objects in relativity, making option C incorrect. ### Revision Summary: - **Relativistic mass increases as speed approaches light speed, becoming infinite at light speed.** - **Exceeding light speed leads to undefined physical scenarios.** - **Sonic booms are not applicable to light-speed travel.** - **Time dilation is relevant only as speeds approach light, not beyond.**