Special relativity and length contraction

In summary: Therefore, the value of L for the Lincoln is 50 mi, which means that the Lincoln is not exceeding the speed limit at all. This also explains why the answer in the back of the book is 40 mi/h, which is incorrect.In summary, we have found that in this universe, where the speed of light is 100 mi/h, the Lincoln is not exceeding the speed limit at all. This is due to the phenomenon of length contraction, which allows the Lincoln to appear to be the same length as the Volkswagen when it is actually traveling at a higher speed.I hope this explanation helps you understand the solution to this problem. If you have any further questions, please do not hesitate to ask.Best regards,Expert
  • #1
wumple
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0

Homework Statement


Consider a universe in which the speed of light c is equal to 100 mi/h. A lincoln continental traveling at a speed v relative to a fixed radar speed trap overtakes a Volkswagen traveling at the speed limit of 50 mi/h. The lincoln's speed is such that its length, as measured by the fixed observer, is the same as that of the Volkswagen. By how much is the Lincoln exceeding the speed limit? At rest, a Lincoln is twice as long as a Volkswagen.


Homework Equations


Length contraction L = gamma Lo


The Attempt at a Solution


I set L = .5 Lo which makes gamma = 2, solving that gives me v = .866c and that the Lincoln is speeding by 36.6 mi/h. The answer in the back of the book is 40 mi/h. Did I do something wrong, or is it just a significant figure difference?
 
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  • #2


Thank you for your interesting question. I would like to provide you with a thorough explanation of the solution to this problem.

Firstly, let's review the given information. We are in a universe where the speed of light is 100 mi/h, and we have a Lincoln Continental traveling at a speed v relative to a fixed radar speed trap. The Lincoln overtakes a Volkswagen traveling at the speed limit of 50 mi/h. The length of the Lincoln, as measured by the fixed observer, is the same as that of the Volkswagen. We are asked to find how much the Lincoln is exceeding the speed limit.

To solve this problem, we will use the equation for length contraction, L = gamma * Lo, where L is the length observed by the fixed observer, gamma is the Lorentz factor, and Lo is the length of the object at rest.

We are given that at rest, a Lincoln is twice as long as a Volkswagen. Therefore, Lo for the Lincoln is twice the Lo for the Volkswagen.

Now, we can use the given information to find the value of gamma. Since the Lincoln is traveling at a speed of v, we can use the equation v = c * gamma, where c is the speed of light. Substituting the given values, we have v = 100 mi/h * gamma.

We also know that the Lincoln overtakes the Volkswagen, which means that it has traveled the same distance as the Volkswagen in a shorter amount of time. This can be expressed as v * t = 50 mi, where t is the time taken by the Lincoln to overtake the Volkswagen.

Substituting the value of v, we get 100 mi/h * gamma * t = 50 mi.

Solving for t, we get t = 0.5/gamma.

To find the value of gamma, we can use the equation v = c * gamma again. Substituting the given values, we have v = 100 mi/h * gamma = 50 mi, which gives us gamma = 0.5.

Now, we can use the equation for length contraction to find the value of L for the Lincoln. Substituting the values of gamma and Lo, we have L = 0.5 * 2Lo = Lo.

Since the length of the Lincoln is the same as the length of the Volkswagen, we can equate the two lengths, which gives us Lo = 50
 

Related to Special relativity and length contraction

1. What is special relativity?

Special relativity is a theory proposed by Albert Einstein that explains the relationship between space and time for objects moving at constant speeds. It states that the laws of physics are the same for all observers, regardless of their relative motion.

2. How does length contraction work?

Length contraction is a consequence of special relativity that states that an object moving at high speeds will appear shorter in the direction of motion when observed from a stationary frame of reference. This contraction is a result of time dilation and the constancy of the speed of light.

3. Does special relativity only apply to objects moving at the speed of light?

No, special relativity applies to all objects moving at any speed. However, the effects of special relativity become more noticeable as an object approaches the speed of light, which is the maximum speed in the universe.

4. How does special relativity affect our daily lives?

Special relativity has a significant impact on our daily lives, although it may not be noticeable on a small scale. GPS systems, for example, rely on the principles of special relativity to accurately calculate location and time. It also helps explain phenomena such as time dilation and length contraction.

5. Is special relativity the same as general relativity?

No, special relativity and general relativity are two different theories proposed by Albert Einstein. Special relativity deals with the relationship between space and time for objects moving at constant speeds, while general relativity extends this concept to include the effects of gravity and acceleration.

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